30-seconds-of-code 中文文档教程
30 seconds of code
精选的有用 JavaScript 片段集合，您可以在 30 秒或更短时间内理解这些片段。
- Use Ctrl + F or command + F to search for a snippet.
- Contributions welcome, please read the contribution guide.
- Snippets are written in ES6, use the Babel transpiler to ensure backwards-compatibility.
- You can import these snippets into VSCode, by following the instructions found here.
- You can search, view and copy these snippets from a terminal, using the CLI application from this repo.
- If you want to follow 30-seconds-of-code on social media, you can find us on Facebook, Instagram and Twitter.
Related projects
- 30 Seconds of CSS
- 30 Seconds of Interviews
- 30 Seconds of React
- 30 Seconds of Python (unofficial)
- 30 Seconds of PHP (unofficial)
Package
⚠️ 注意：一些我们的片段尚未针对生产进行优化（请参阅个别片段问题的免责声明）。
您可以在 npm 上找到包含所有片段的包。
# With npm
npm install 30-seconds-of-code
# With yarn
yarn add 30-seconds-of-code
Details
浏览器
<script src="https://unpkg.com/30-seconds-of-code@1/dist/_30s.es5.min.js"></script>
<script>
_30s.average(1, 2, 3);
</script>
节点
// CommonJS
const _30s = require('30-seconds-of-code');
_30s.average(1, 2, 3);
// ES Modules
import _30s from '30-seconds-of-code';
_30s.average(1, 2, 3);
Contents
Adapter
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Array
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allallEqualanyarrayToCSVbifurcatebifurcateBychunkcompactcountBycountOccurrencesdeepFlattendifferencedifferenceBydifferenceWithdropdropRightdropRightWhiledropWhileeveryNthfilterNonUniquefilterNonUniqueByfindLastfindLastIndexflattenforEachRightgroupByheadindexOfAllinitialinitialize2DArrayinitializeArrayWithRangeinitializeArrayWithRangeRightinitializeArrayWithValuesinitializeNDArrayintersectionintersectionByintersectionWithisSortedjoinJSONtoCSVlastlongestItemmapObjectmaxNminNnonenthElementoffsetpartitionpermutationspullpullAtIndexpullAtValuepullByreducedFilterreduceSuccessivereduceWhichrejectremovesamplesampleSizeshankshufflesimilaritysortedIndexsortedIndexBysortedLastIndexsortedLastIndexBystableSortsymmetricDifferencesymmetricDifferenceBysymmetricDifferenceWithtailtaketakeRighttakeRightWhiletakeWhiletoHashunionunionByunionWithuniqueElementsuniqueElementsByuniqueElementsByRightuniqueSymmetricDifferenceunzipunzipWithwithoutxProdzipzipObjectzipWith
Browser
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arrayToHtmlListbottomVisiblecopyToClipboardcountercreateElementcreateEventHubcurrentURLdetectDeviceTypeelementContainselementIsVisibleInViewportgetImagesgetScrollPositiongetStylehasClasshashBrowserhidehttpsRedirectinsertAfterinsertBeforeisBrowserTabFocusednodeListToArrayobserveMutationsoffononUserInputChangeprefixrecordAnimationFramesredirectrunAsyncscrollToTopsetStyleshowsmoothScrolltoggleClasstriggerEventUUIDGeneratorBrowser
⏱️ Date
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????️ Function
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➗ Math
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approximatelyEqualaverageaverageBybinomialCoefficientclampNumberdegreesToRadsdigitizedistanceelofactorialfibonaccigcdgeometricProgressionhammingDistanceinRangeisDivisibleisEvenisNegativeZeroisPrimelcmluhnCheckmaxBymedianminBypercentilepowersetprimesradsToDegreesrandomIntArrayInRangerandomIntegerInRangerandomNumberInRangeroundsdbmstandardDeviationsumsumBysumPowertoSafeInteger
Node
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????️ Object
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String
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byteSizecapitalizecapitalizeEveryWordCSVToArrayCSVToJSONdecapitalizeescapeHTMLescapeRegExpfromCamelCaseindentStringisAbsoluteURLisAnagramisLowerCaseisUpperCasemapStringmaskpadpalindromepluralizeremoveNonASCIIreverseStringsortCharactersInStringsplitLinesstringPermutationsstripHTMLTagstoCamelCasetoKebabCasetoSnakeCasetoTitleCasetruncateStringunescapeHTMLURLJoinwords
Type
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Utility
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Adapter
ary
创建一个最多接受 n 个参数的函数，忽略任何其他参数。
使用 Array.prototype.slice(0,n) 和扩展运算符 ( <代码>...）。
const ary = (fn, n) => (...args) => fn(...args.slice(0, n));
Examples
const firstTwoMax = ary(Math.max, 2);
[[2, 6, 'a'], [8, 4, 6], [10]].map(x => firstTwoMax(...x)); // [6, 8, 10]
call
给定一个键和一组参数，在给定上下文时调用它们。 主要用于组合。
使用闭包调用带有存储参数的存储键。
const call = (key, ...args) => context => context[key](...args);
Examples
Promise.resolve([1, 2, 3])
.then(call('map', x => 2 * x))
.then(console.log); // [ 2, 4, 6 ]
const map = call.bind(null, 'map');
Promise.resolve([1, 2, 3])
.then(map(x => 2 * x))
.then(console.log); // [ 2, 4, 6 ]
collectInto
将接受数组的函数更改为可变参数函数。
给定一个函数，返回一个将所有输入收集到数组接受函数中的闭包。
const collectInto = fn => (...args) => fn(args);
Examples
const Pall = collectInto(Promise.all.bind(Promise));
let p1 = Promise.resolve(1);
let p2 = Promise.resolve(2);
let p3 = new Promise(resolve => setTimeout(resolve, 2000, 3));
Pall(p1, p2, p3).then(console.log); // [1, 2, 3] (after about 2 seconds)
flip
Flip 将函数作为参数，然后将第一个参数作为最后一个参数。
返回一个接受可变输入的闭包，并在应用其余参数之前拼接最后一个参数使其成为第一个参数。
const flip = fn => (first, ...rest) => fn(...rest, first);
Examples
let a = { name: 'John Smith' };
let b = {};
const mergeFrom = flip(Object.assign);
let mergePerson = mergeFrom.bind(null, a);
mergePerson(b); // == b
b = {};
Object.assign(b, a); // == b
over
创建一个函数，该函数使用它接收的参数调用每个提供的函数并返回结果。
使用 Array.prototype.map() 和 Function.prototype.apply() 将每个函数应用于给定的参数。
const over = (...fns) => (...args) => fns.map(fn => fn.apply(null, args));
Examples
const minMax = over(Math.min, Math.max);
minMax(1, 2, 3, 4, 5); // [1,5]
overArgs
创建一个调用提供的函数并转换其参数的函数。
使用 Array.prototype.map() 将 transforms 应用到 args 并结合扩展运算符 (...) 将转换后的参数传递给 fn。
const overArgs = (fn, transforms) => (...args) => fn(...args.map((val, i) => transforms[i](val)));
Examples
const square = n => n * n;
const double = n => n * 2;
const fn = overArgs((x, y) => [x, y], [square, double]);
fn(9, 3); // [81, 6]
pipeAsyncFunctions
为异步函数执行从左到右的函数组合。
将 Array.prototype.reduce() 与扩展运算符 (...) 结合使用，以使用 Promise.then()< 执行从左到右的函数组合/代码>。 这些函数可以返回以下组合：简单值、Promise，或者它们可以定义为通过 await 返回的async。 所有函数都必须是一元的。
const pipeAsyncFunctions = (...fns) => arg => fns.reduce((p, f) => p.then(f), Promise.resolve(arg));
Examples
const sum = pipeAsyncFunctions(
x => x + 1,
x => new Promise(resolve => setTimeout(() => resolve(x + 2), 1000)),
x => x + 3,
async x => (await x) + 4
);
(async() => {
console.log(await sum(5)); // 15 (after one second)
})();
pipeFunctions
执行从左到右的函数组合。
将 Array.prototype.reduce() 与扩展运算符 (...) 一起使用，以执行从左到右的函数组合。 第一个（最左边的）函数可以接受一个或多个参数； 其余函数必须是一元的。
const pipeFunctions = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));
Examples
const add5 = x => x + 5;
const multiply = (x, y) => x * y;
const multiplyAndAdd5 = pipeFunctions(multiply, add5);
multiplyAndAdd5(5, 2); // 15
promisify
将异步函数转换为返回承诺。
使用柯里化返回一个函数，该函数返回调用原始函数的 Promise。 使用 ...rest 运算符传入所有参数。
在 Node 8+ 中，您可以使用 util.promisify
const promisify = func => (...args) =>
new Promise((resolve, reject) =>
func(...args, (err, result) => (err ? reject(err) : resolve(result)))
);
Examples
const delay = promisify((d, cb) => setTimeout(cb, d));
delay(2000).then(() => console.log('Hi!')); // // Promise resolves after 2s
rearg
创建一个调用提供的函数的函数，其参数根据指定的索引排列。
使用 Array.prototype.map() 根据 indexes 结合扩展运算符 (...) 对参数重新排序以传递转换后的结果fn 的参数。
const rearg = (fn, indexes) => (...args) => fn(...indexes.map(i => args[i]));
Examples
var rearged = rearg(
function(a, b, c) {
return [a, b, c];
},
[2, 0, 1]
);
rearged('b', 'c', 'a'); // ['a', 'b', 'c']
spreadOver
获取可变参数函数并返回一个闭包，该闭包接受要映射到函数输入的参数数组。
使用闭包和扩展运算符 (...) 将参数数组映射到函数的输入。
const spreadOver = fn => argsArr => fn(...argsArr);
Examples
const arrayMax = spreadOver(Math.max);
arrayMax([1, 2, 3]); // 3
unary
创建一个最多接受一个参数的函数，忽略任何其他参数。
调用提供的函数 fn，仅使用给定的第一个参数。
const unary = fn => val => fn(val);
Examples
['6', '8', '10'].map(unary(parseInt)); // [6, 8, 10]
Array
all
如果提供的谓词函数对集合中的所有元素返回 true，则返回 true， false 否则。
使用 Array.prototype.every() 测试集合中的所有元素是否根据 fn 返回 true。 省略第二个参数 fn，以使用 Boolean 作为默认值。
const all = (arr, fn = Boolean) => arr.every(fn);
Examples
all([4, 2, 3], x => x > 1); // true
all([1, 2, 3]); // true
allEqual
检查数组中的所有元素是否相等。
使用 Array.prototype.every() 检查数组的所有元素是否都与第一个元素相同。
const allEqual = arr => arr.every(val => val === arr[0]);
Examples
allEqual([1, 2, 3, 4, 5, 6]); // false
allEqual([1, 1, 1, 1]); // true
any
如果提供的谓词函数对 a 中的至少一个元素返回 true，则返回 true集合，否则为 false。
使用 Array.prototype.some() 测试集合中的任何元素是否根据 fn 返回 true。 省略第二个参数 fn，以使用 Boolean 作为默认值。
const any = (arr, fn = Boolean) => arr.some(fn);
Examples
any([0, 1, 2, 0], x => x >= 2); // true
any([0, 0, 1, 0]); // true
arrayToCSV
将二维数组转换为逗号分隔值 (CSV) 字符串。
使用 Array.prototype.map() 和 Array.prototype.join(delimiter) 将单个一维数组（行）组合成字符串。 使用 Array.prototype.join('\n') 将所有行组合成一个 CSV 字符串，每行用换行符分隔。 省略第二个参数 delimiter，以使用默认分隔符 ,。
const arrayToCSV = (arr, delimiter = ',') =>
arr.map(v => v.map(x => `"${x}"`).join(delimiter)).join('\n');
Examples
arrayToCSV([['a', 'b'], ['c', 'd']]); // '"a","b"\n"c","d"'
arrayToCSV([['a', 'b'], ['c', 'd']], ';'); // '"a";"b"\n"c";"d"'
⬆ 返回页首 将
bifurcate
值分成两组。 如果filter中的元素为真，则集合中对应的元素属于第一组； 否则，它属于第二组。
使用 Array.prototype.reduce() 和 Array.prototype.push() 基于 filter 将元素添加到组中。
const bifurcate = (arr, filter) =>
arr.reduce((acc, val, i) => (acc[filter[i] ? 0 : 1].push(val), acc), [[], []]);
Examples
bifurcate(['beep', 'boop', 'foo', 'bar'], [true, true, false, true]); // [ ['beep', 'boop', 'bar'], ['foo'] ]
bifurcateBy
根据谓词函数将值分成两组，谓词函数指定输入集合中的元素属于哪一组。 如果谓词函数返回真值，则集合元素属于第一组； 否则，它属于第二组。
根据 fn 返回的值，使用 Array.prototype.reduce() 和 Array.prototype.push() 将元素添加到组中对于每个元素。
const bifurcateBy = (arr, fn) =>
arr.reduce((acc, val, i) => (acc[fn(val, i) ? 0 : 1].push(val), acc), [[], []]);
Examples
bifurcateBy(['beep', 'boop', 'foo', 'bar'], x => x[0] === 'b'); // [ ['beep', 'boop', 'bar'], ['foo'] ]
chunk
将数组分块为指定大小的较小数组。
使用 Array.from() 创建一个新数组，该数组适合将要生成的块数。 使用 Array.prototype.slice() 将新数组的每个元素映射到长度为 size 的块。 如果原始数组不能被平均分割，最后的块将包含剩余的元素。
const chunk = (arr, size) =>
Array.from({ length: Math.ceil(arr.length / size) }, (v, i) =>
arr.slice(i * size, i * size + size)
);
Examples
chunk([1, 2, 3, 4, 5], 2); // [[1,2],[3,4],[5]]
compact
从数组中删除假值。
使用 Array.prototype.filter() 过滤掉虚假值（false、null、0、""、未定义 和 NaN）。
const compact = arr => arr.filter(Boolean);
Examples
compact([0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34]); // [ 1, 2, 3, 'a', 's', 34 ]
countBy
根据给定的函数对数组的元素进行分组，并返回每组中元素的数量。
使用 Array.prototype.map() 将数组的值映射到函数或属性名称。 使用 Array.prototype.reduce() 创建一个对象，其中的键是根据映射结果生成的。
const countBy = (arr, fn) =>
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => {
acc[val] = (acc[val] || 0) + 1;
return acc;
}, {});
Examples
countBy([6.1, 4.2, 6.3], Math.floor); // {4: 1, 6: 2}
countBy(['one', 'two', 'three'], 'length'); // {3: 2, 5: 1}
countOccurrences
计算数组中某个值的出现次数。
每次遇到数组中的特定值时，使用 Array.prototype.reduce() 递增计数器。
const countOccurrences = (arr, val) => arr.reduce((a, v) => (v === val ? a + 1 : a), 0);
Examples
countOccurrences([1, 1, 2, 1, 2, 3], 1); // 3
deepFlatten
Deep 展平数组。
使用递归。 将 Array.prototype.concat() 与一个空数组 ([]) 和扩展运算符 (...) 结合使用来展平数组. 递归地展平数组中的每个元素。
const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));
Examples
deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5]
difference
返回两个数组之间的差异。
从 b 创建一个 Set，然后在 a 上使用 Array.prototype.filter() 只保留值而不是包含在 b 中。
const difference = (a, b) => {
const s = new Set(b);
return a.filter(x => !s.has(x));
};
Examples
difference([1, 2, 3], [1, 2, 4]); // [3]
differenceBy
在将提供的函数应用于两个数组的每个数组元素后，返回两个数组之间的差异。
通过对 b 中的每个元素应用 fn 创建一个 Set，然后在中使用 Array.prototype.filter()与 a 上的 fn 结合，只保留不包含在先前创建的集合中的值。
const differenceBy = (a, b, fn) => {
const s = new Set(b.map(fn));
return a.filter(x => !s.has(fn(x)));
};
Examples
differenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [1.2]
differenceBy([{ x: 2 }, { x: 1 }], [{ x: 1 }], v => v.x); // [ { x: 2 } ]
differenceWith
从比较器函数不返回 true 的数组中过滤掉所有值。
使用 Array.prototype.filter() 和 Array.prototype.findIndex() 找到合适的值。
const differenceWith = (arr, val, comp) => arr.filter(a => val.findIndex(b => comp(a, b)) === -1);
Examples
differenceWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0], (a, b) => Math.round(a) === Math.round(b)); // [1, 1.2]
drop
返回一个新数组，其中 n 个元素从左侧移除。
使用 Array.prototype.slice() 切片并从左侧移除指定数量的元素。
const drop = (arr, n = 1) => arr.slice(n);
Examples
drop([1, 2, 3]); // [2,3]
drop([1, 2, 3], 2); // [3]
drop([1, 2, 3], 42); // []
dropRight
返回一个新数组，其中 n 个元素从右侧移除。
使用 Array.prototype.slice() 切片并从右侧移除指定数量的元素。
const dropRight = (arr, n = 1) => arr.slice(0, -n);
Examples
dropRight([1, 2, 3]); // [1,2]
dropRight([1, 2, 3], 2); // [1]
dropRight([1, 2, 3], 42); // []
dropRightWhile
从数组末尾删除元素，直到传递的函数返回 true。 返回数组中的剩余元素。
遍历数组，使用 Array.prototype.slice() 删除数组的最后一个元素，直到函数的返回值为 true。 返回剩余的元素。
const dropRightWhile = (arr, func) => {
while (arr.length > 0 && !func(arr[arr.length - 1])) arr = arr.slice(0, -1);
return arr;
};
Examples
dropRightWhile([1, 2, 3, 4], n => n < 3); // [1, 2]
dropWhile
删除数组中的元素，直到传递的函数返回 true。 返回数组中的剩余元素。
遍历数组，使用 Array.prototype.slice() 删除数组的第一个元素，直到函数的返回值为 true。 返回剩余的元素。
const dropWhile = (arr, func) => {
while (arr.length > 0 && !func(arr[0])) arr = arr.slice(1);
return arr;
};
Examples
dropWhile([1, 2, 3, 4], n => n >= 3); // [3,4]
everyNth
返回数组中的第 n 个元素。
使用 Array.prototype.filter() 创建一个包含给定数组的每个第 n 个元素的新数组。
const everyNth = (arr, nth) => arr.filter((e, i) => i % nth === nth - 1);
Examples
everyNth([1, 2, 3, 4, 5, 6], 2); // [ 2, 4, 6 ]
filterNonUnique
过滤掉数组中的非唯一值。
对仅包含唯一值的数组使用 Array.prototype.filter()。
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
Examples
filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1, 3, 5]
filterNonUniqueBy
根据提供的比较器函数过滤掉数组中的非唯一值。
根据比较函数 fn<，将 Array.prototype.filter() 和 Array.prototype.every() 用于仅包含唯一值的数组/代码>。 比较器函数有四个参数：被比较的两个元素的值和它们的索引。
const filterNonUniqueBy = (arr, fn) =>
arr.filter((v, i) => arr.every((x, j) => (i === j) === fn(v, x, i, j)));
Examples
filterNonUniqueBy(
[
{ id: 0, value: 'a' },
{ id: 1, value: 'b' },
{ id: 2, value: 'c' },
{ id: 1, value: 'd' },
{ id: 0, value: 'e' }
],
(a, b) => a.id == b.id
); // [ { id: 2, value: 'c' } ]
findLast
返回所提供的函数为其返回真值的最后一个元素。
使用 Array.prototype.filter() 删除 fn 返回错误值的元素，使用 Array.prototype.pop() 获取最后一个一。
const findLast = (arr, fn) => arr.filter(fn).pop();
Examples
findLast([1, 2, 3, 4], n => n % 2 === 1); // 3
findLastIndex
返回最后一个元素的索引，所提供的函数为其返回真值。
使用 Array.prototype.map() 将每个元素映射到一个数组及其索引和值。 使用 Array.prototype.filter() 删除 fn 返回错误值的元素，使用 Array.prototype.pop() 获取最后一个一。
const findLastIndex = (arr, fn) =>
arr
.map((val, i) => [i, val])
.filter(([i, val]) => fn(val, i, arr))
.pop()[0];
Examples
findLastIndex([1, 2, 3, 4], n => n % 2 === 1); // 2 (index of the value 3)
flatten
将数组展平到指定深度。
使用递归，将每个深度级别的 depth 递减 1。 使用 Array.prototype.reduce() 和 Array.prototype.concat() 合并元素或数组。 基本情况，对于 depth 等于 1 停止递归。 省略第二个参数 depth 以仅展平到 1 的深度（单次展平）。
const flatten = (arr, depth = 1) =>
arr.reduce((a, v) => a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v), []);
Examples
flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]
forEachRight
从数组的最后一个元素开始，为每个数组元素执行一次提供的函数。
使用 Array.prototype.slice(0) 克隆给定的数组，使用 Array.prototype.reverse() 反转它，使用 Array.prototype.forEach() 遍历反转数组。
const forEachRight = (arr, callback) =>
arr
.slice(0)
.reverse()
.forEach(callback);
Examples
forEachRight([1, 2, 3, 4], val => console.log(val)); // '4', '3', '2', '1'
groupBy
根据给定函数对数组元素进行分组。
使用 Array.prototype.map() 将数组的值映射到函数或属性名称。 使用 Array.prototype.reduce() 创建一个对象，其中的键是根据映射结果生成的。
const groupBy = (arr, fn) =>
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val, i) => {
acc[val] = (acc[val] || []).concat(arr[i]);
return acc;
}, {});
Examples
groupBy([6.1, 4.2, 6.3], Math.floor); // {4: [4.2], 6: [6.1, 6.3]}
groupBy(['one', 'two', 'three'], 'length'); // {3: ['one', 'two'], 5: ['three']}
head
返回列表的头部。
使用 arr[0] 返回传入数组的第一个元素。
const head = arr => arr[0];
Examples
head([1, 2, 3]); // 1
indexOfAll
返回数组中 val 的所有索引。 如果 val 从未发生，则返回 []。
使用 Array.prototype.reduce() 遍历元素并存储匹配元素的索引。 返回索引数组。
const indexOfAll = (arr, val) => arr.reduce((acc, el, i) => (el === val ? [...acc, i] : acc), []);
Examples
indexOfAll([1, 2, 3, 1, 2, 3], 1); // [0,3]
indexOfAll([1, 2, 3], 4); // []
initial
返回数组中除最后一个元素之外的所有元素。
使用 arr.slice(0,-1) 返回数组中除最后一个元素之外的所有元素。
const initial = arr => arr.slice(0, -1);
Examples
initial([1, 2, 3]); // [1,2]
initialize2DArray
初始化给定宽度、高度和值的二维数组。
使用 Array.prototype.map() 生成 h 行，其中每行都是一个大小为 w 并用值初始化的新数组。 如果未提供该值，则默认为 null。
const initialize2DArray = (w, h, val = null) =>
Array.from({ length: h }).map(() => Array.from({ length: w }).fill(val));
Examples
initialize2DArray(2, 2, 0); // [[0,0], [0,0]]
initializeArrayWithRange
初始化一个包含指定范围内的数字的数组，其中 start 和 end 包括在内它们的共同区别是 step。
使用 Array.from() 创建所需长度的数组，(end - start + 1)/step，并使用 map 函数用所需的值填充数组在给定的范围内。 您可以省略 start 以使用默认值 0。 您可以省略 step 以使用默认值 1。
const initializeArrayWithRange = (end, start = 0, step = 1) =>
Array.from({ length: Math.ceil((end - start + 1) / step) }, (v, i) => i * step + start);
Examples
initializeArrayWithRange(5); // [0,1,2,3,4,5]
initializeArrayWithRange(7, 3); // [3,4,5,6,7]
initializeArrayWithRange(9, 0, 2); // [0,2,4,6,8]
initializeArrayWithRangeRight
初始化一个数组，其中包含指定范围内的数字（反向），其中 start 和 end code> 包含它们的共同区别 step。
使用 Array.from(Math.ceil((end+1-start)/step)) 创建所需长度的数组（元素数量等于 (end-start )/step 或 (end+1-start)/step 包含结束), Array.prototype.map() 填充所需的值一个范围。 您可以省略 start 以使用默认值 0。 您可以省略 step 以使用默认值 1。
const initializeArrayWithRangeRight = (end, start = 0, step = 1) =>
Array.from({ length: Math.ceil((end + 1 - start) / step) }).map(
(v, i, arr) => (arr.length - i - 1) * step + start
);
Examples
initializeArrayWithRangeRight(5); // [5,4,3,2,1,0]
initializeArrayWithRangeRight(7, 3); // [7,6,5,4,3]
initializeArrayWithRangeRight(9, 0, 2); // [8,6,4,2,0]
initializeArrayWithValues
初始化数组并用指定值填充数组。
使用 Array(n) 创建所需长度的数组，使用 fill(v) 用所需的值填充它。 您可以省略 val 以使用默认值 0。
const initializeArrayWithValues = (n, val = 0) => Array(n).fill(val);
Examples
initializeArrayWithValues(5, 2); // [2, 2, 2, 2, 2]
initializeNDArray
创建一个具有给定值的 n 维数组。
使用递归。 使用 Array.prototype.map() 生成行，其中每行都是使用 initializeNDArray 初始化的新数组。
const initializeNDArray = (val, ...args) =>
args.length === 0
? val
: Array.from({ length: args[0] }).map(() => initializeNDArray(val, ...args.slice(1)));
Examples
initializeNDArray(1, 3); // [1,1,1]
initializeNDArray(5, 2, 2, 2); // [[[5,5],[5,5]],[[5,5],[5,5]]]
intersection
返回两个数组中都存在的元素列表。
从 b 创建一个 Set，然后在 a 上使用 Array.prototype.filter() 以仅保留包含的值在 b 中。
const intersection = (a, b) => {
const s = new Set(b);
return a.filter(x => s.has(x));
};
Examples
intersection([1, 2, 3], [4, 3, 2]); // [2, 3]
intersectionBy
在将提供的函数应用于两个数组的每个数组元素后，返回两个数组中都存在的元素列表。
通过将 fn 应用于 b 中的所有元素来创建一个 Set，然后使用 Array.prototype.filter() a 只保留元素，当 fn 应用于它们时，这些元素会产生包含在 b 中的值。
const intersectionBy = (a, b, fn) => {
const s = new Set(b.map(fn));
return a.filter(x => s.has(fn(x)));
};
Examples
intersectionBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [2.1]
intersectionWith
使用提供的比较函数返回两个数组中都存在的元素列表。
将 Array.prototype.filter() 和 Array.prototype.findIndex() 与提供的比较器结合使用以确定相交值。
const intersectionWith = (a, b, comp) => a.filter(x => b.findIndex(y => comp(x, y)) !== -1);
Examples
intersectionWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b)); // [1.5, 3, 0]
isSorted
如果数组按升序排序，则返回 1，否则返回 -1按降序排序，如果未排序，则为 0。
计算前两个元素的排序 direction。 使用 Object.entries() 遍历数组对象并成对比较它们。 如果 direction 发生变化，则返回 0；如果到达最后一个元素，则返回 direction。
const isSorted = arr => {
let direction = -(arr[0] - arr[1]);
for (let [i, val] of arr.entries()) {
direction = !direction ? -(arr[i - 1] - arr[i]) : direction;
if (i === arr.length - 1) return !direction ? 0 : direction;
else if ((val - arr[i + 1]) * direction > 0) return 0;
}
};
Examples
isSorted([0, 1, 2, 2]); // 1
isSorted([4, 3, 2]); // -1
isSorted([4, 3, 5]); // 0
join
将数组的所有元素连接成一个字符串并返回该字符串。 使用分隔符和结束分隔符。
使用 Array.prototype.reduce() 将元素组合成一个字符串。 省略第二个参数 separator，以使用默认分隔符 ','。 省略第三个参数 end，默认使用与 separator 相同的值。
const join = (arr, separator = ',', end = separator) =>
arr.reduce(
(acc, val, i) =>
i === arr.length - 2
? acc + val + end
: i === arr.length - 1
? acc + val
: acc + val + separator,
''
);
Examples
join(['pen', 'pineapple', 'apple', 'pen'], ',', '&'); // "pen,pineapple,apple&pen"
join(['pen', 'pineapple', 'apple', 'pen'], ','); // "pen,pineapple,apple,pen"
join(['pen', 'pineapple', 'apple', 'pen']); // "pen,pineapple,apple,pen"
JSONtoCSV 
将对象数组转换为逗号分隔值 (CSV) 字符串，该字符串仅包含指定的列。
使用 Array.prototype.join(delimiter) 组合 columns 中的所有名称以创建第一行。 使用 Array.prototype.map() 和 Array.prototype.reduce() 为每个对象创建一行，将不存在的值替换为空字符串和仅映射值在列中。 使用 Array.prototype.join('\n') 将所有行组合成一个字符串。 省略第三个参数 delimiter，以使用默认分隔符 ,。
const JSONtoCSV = (arr, columns, delimiter = ',') =>
[
columns.join(delimiter),
...arr.map(obj =>
columns.reduce(
(acc, key) => `${acc}${!acc.length ? '' : delimiter}"${!obj[key] ? '' : obj[key]}"`,
''
)
)
].join('\n');
Examples
JSONtoCSV([{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }], ['a', 'b']); // 'a,b\n"1","2"\n"3","4"\n"6",""\n"","7"'
JSONtoCSV([{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }], ['a', 'b'], ';'); // 'a;b\n"1";"2"\n"3";"4"\n"6";""\n"";"7"'
last
返回数组中的最后一个元素。
使用 arr.length - 1 计算给定数组最后一个元素的索引并返回它。
const last = arr => arr[arr.length - 1];
Examples
last([1, 2, 3]); // 3
longestItem
获取任意数量的可迭代对象或具有 length 属性的对象并返回最长的一个。 如果多个对象的长度相同，则返回第一个。 如果未提供参数，则返回 undefined。
使用Array.prototype.reduce()，比较对象的length，找出最长的一个。
const longestItem = (...vals) => vals.reduce((a, x) => (x.length > a.length ? x : a));
Examples
longestItem('this', 'is', 'a', 'testcase'); // 'testcase'
longestItem(...['a', 'ab', 'abc']); // 'abc'
longestItem(...['a', 'ab', 'abc'], 'abcd'); // 'abcd'
longestItem([1, 2, 3], [1, 2], [1, 2, 3, 4, 5]); // [1, 2, 3, 4, 5]
longestItem([1, 2, 3], 'foobar'); // 'foobar'
mapObject
使用函数将数组的值映射到对象，其中键值对由作为键的原始值和映射的值组成价值。
使用匿名内部函数范围声明未定义的内存空间，使用闭包存储返回值。 使用新的 Array 来存储数组及其数据集上的函数映射和逗号运算符以返回第二步，而无需从一个上下文移动到另一个上下文（由于闭包和顺序的操作）。
const mapObject = (arr, fn) =>
(a => (
(a = [arr, arr.map(fn)]), a[0].reduce((acc, val, ind) => ((acc[val] = a[1][ind]), acc), {})
))();
Examples
const squareIt = arr => mapObject(arr, a => a * a);
squareIt([1, 2, 3]); // { 1: 1, 2: 4, 3: 9 }
maxN
从提供的数组中返回 n 个最大元素。 如果 n 大于或等于提供的数组长度，则返回原始数组（按降序排序）。
使用 Array.prototype.sort() 结合扩展运算符 (...) 创建数组的浅表克隆并按降序对其进行排序。 使用 Array.prototype.slice() 获取指定数量的元素。 省略第二个参数 n，以获得单元素数组。
const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n);
Examples
maxN([1, 2, 3]); // [3]
maxN([1, 2, 3], 2); // [3,2]
minN
从提供的数组中返回 n 个最小元素。 如果 n 大于或等于提供的数组长度，则返回原始数组（按升序排序）。
使用 Array.prototype.sort() 结合扩展运算符 (...) 创建数组的浅表克隆并按升序对其进行排序。 使用 Array.prototype.slice() 获取指定数量的元素。 省略第二个参数 n，以获得单元素数组。
const minN = (arr, n = 1) => [...arr].sort((a, b) => a - b).slice(0, n);
Examples
minN([1, 2, 3]); // [1]
minN([1, 2, 3], 2); // [1,2]
none
如果提供的谓词函数对集合中的所有元素返回 false，则返回 true， false 否则。
使用 Array.prototype.some() 测试集合中的任何元素是否根据 fn 返回 true。 省略第二个参数 fn，以使用 Boolean 作为默认值。
const none = (arr, fn = Boolean) => !arr.some(fn);
Examples
none([0, 1, 3, 0], x => x == 2); // true
none([0, 0, 0]); // true
nthElement
返回数组的第 n 个元素。
使用 Array.prototype.slice() 获取第一个包含第 n 个元素的数组。 如果索引超出范围，则返回 undefined。 省略第二个参数 n，以获取数组的第一个元素。
const nthElement = (arr, n = 0) => (n === -1 ? arr.slice(n) : arr.slice(n, n + 1))[0];
Examples
nthElement(['a', 'b', 'c'], 1); // 'b'
nthElement(['a', 'b', 'b'], -3); // 'a'
offset
将指定数量的元素移动到数组末尾。
使用 Array.prototype.slice() 两次获取指定索引之后的元素和之前的元素。 使用扩展运算符 (...) 将两者组合成一个数组。 如果 offset 为负数，元素将从末尾移动到开始。
const offset = (arr, offset) => [...arr.slice(offset), ...arr.slice(0, offset)];
Examples
offset([1, 2, 3, 4, 5], 2); // [3, 4, 5, 1, 2]
offset([1, 2, 3, 4, 5], -2); // [4, 5, 1, 2, 3]
partition
根据提供的函数对每个元素的真实性，将元素分组到两个数组中。
使用 Array.prototype.reduce() 创建一个包含两个数组的数组。 使用 Array.prototype.push() 将 fn 返回 true 的元素添加到第一个数组和 fn< /code> 返回 false 给第二个。
const partition = (arr, fn) =>
arr.reduce(
(acc, val, i, arr) => {
acc[fn(val, i, arr) ? 0 : 1].push(val);
return acc;
},
[[], []]
);
Examples
const users = [{ user: 'barney', age: 36, active: false }, { user: 'fred', age: 40, active: true }];
partition(users, o => o.active); // [[{ 'user': 'fred', 'age': 40, 'active': true }],[{ 'user': 'barney', 'age': 36, 'active': false }]]
permutations
⚠️ 警告：此函数的执行时间随每个数组元素呈指数增长。 超过 8 到 10 个条目将导致您的浏览器在尝试解决所有不同组合时挂起。
生成数组元素的所有排列（包含重复项）。
使用递归。 对于给定数组中的每个元素，为其其余元素创建所有部分排列。 使用 Array.prototype.map() 将元素与每个部分排列组合，然后使用 Array.prototype.reduce() 将所有排列组合到一个数组中。 基本情况是数组 length 等于 2 或 1。
const permutations = arr => {
if (arr.length <= 2) return arr.length === 2 ? [arr, [arr[1], arr[0]]] : arr;
return arr.reduce(
(acc, item, i) =>
acc.concat(
permutations([...arr.slice(0, i), ...arr.slice(i + 1)]).map(val => [item, ...val])
),
[]
);
};
Examples
permutations([1, 33, 5]); // [ [ 1, 33, 5 ], [ 1, 5, 33 ], [ 33, 1, 5 ], [ 33, 5, 1 ], [ 5, 1, 33 ], [ 5, 33, 1 ] ]
pull
改变原始数组以过滤掉指定的值。
使用 Array.prototype.filter() 和 Array.prototype.includes() 提取不需要的值。 使用 Array.prototype.length = 0 通过将其长度重置为零来改变传入的数组，并使用 Array.prototype.push() 重新填充它拉取的值。
（对于不改变原始数组的片段，请参阅without）
const pull = (arr, ...args) => {
let argState = Array.isArray(args[0]) ? args[0] : args;
let pulled = arr.filter((v, i) => !argState.includes(v));
arr.length = 0;
pulled.forEach(v => arr.push(v));
};
Examples
let myArray = ['a', 'b', 'c', 'a', 'b', 'c'];
pull(myArray, 'a', 'c'); // myArray = [ 'b', 'b' ]
pullAtIndex
改变原始数组以过滤掉指定索引处的值。
使用 Array.prototype.filter() 和 Array.prototype.includes() 提取不需要的值。 使用 Array.prototype.length = 0 通过将其长度重置为零来改变传入的数组，并使用 Array.prototype.push() 重新填充它拉取的值。 使用 Array.prototype.push() 跟踪提取的值
const pullAtIndex = (arr, pullArr) => {
let removed = [];
let pulled = arr
.map((v, i) => (pullArr.includes(i) ? removed.push(v) : v))
.filter((v, i) => !pullArr.includes(i));
arr.length = 0;
pulled.forEach(v => arr.push(v));
return removed;
};
Examples
let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtIndex(myArray, [1, 3]); // myArray = [ 'a', 'c' ] , pulled = [ 'b', 'd' ]
pullAtValue
改变原始数组以过滤掉指定的值。 返回删除的元素。
使用 Array.prototype.filter() 和 Array.prototype.includes() 提取不需要的值。 使用 Array.prototype.length = 0 通过将其长度重置为零来改变传入的数组，并使用 Array.prototype.push() 重新填充它拉取的值。 使用 Array.prototype.push() 跟踪提取的值
const pullAtValue = (arr, pullArr) => {
let removed = [],
pushToRemove = arr.forEach((v, i) => (pullArr.includes(v) ? removed.push(v) : v)),
mutateTo = arr.filter((v, i) => !pullArr.includes(v));
arr.length = 0;
mutateTo.forEach(v => arr.push(v));
return removed;
};
Examples
let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtValue(myArray, ['b', 'd']); // myArray = [ 'a', 'c' ] , pulled = [ 'b', 'd' ]
pullBy
根据给定的迭代器函数，改变原始数组以过滤掉指定的值。
检查函数中是否提供了最后一个参数。 使用 Array.prototype.map() 将迭代器函数 fn 应用于所有数组元素。 使用 Array.prototype.filter() 和 Array.prototype.includes() 提取不需要的值。 使用 Array.prototype.length = 0 通过将其长度重置为零来改变传入的数组，并使用 Array.prototype.push() 重新填充它拉取的值。
const pullBy = (arr, ...args) => {
const length = args.length;
let fn = length > 1 ? args[length - 1] : undefined;
fn = typeof fn == 'function' ? (args.pop(), fn) : undefined;
let argState = (Array.isArray(args[0]) ? args[0] : args).map(val => fn(val));
let pulled = arr.filter((v, i) => !argState.includes(fn(v)));
arr.length = 0;
pulled.forEach(v => arr.push(v));
};
Examples
var myArray = [{ x: 1 }, { x: 2 }, { x: 3 }, { x: 1 }];
pullBy(myArray, [{ x: 1 }, { x: 3 }], o => o.x); // myArray = [{ x: 2 }]
reducedFilter
根据条件过滤对象数组，同时过滤掉未指定的键。
使用 Array.prototype.filter() 根据谓词 fn 过滤数组，以便它返回条件返回真值的对象。 在过滤后的数组上，使用 Array.prototype.map() 返回新对象，使用 Array.prototype.reduce() 过滤掉未提供的键keys 参数。
const reducedFilter = (data, keys, fn) =>
data.filter(fn).map(el =>
keys.reduce((acc, key) => {
acc[key] = el[key];
return acc;
}, {})
);
Examples
const data = [
{
id: 1,
name: 'john',
age: 24
},
{
id: 2,
name: 'mike',
age: 50
}
];
reducedFilter(data, ['id', 'name'], item => item.age > 24); // [{ id: 2, name: 'mike'}]
reduceSuccessive
对累加器和数组中的每个元素应用一个函数（从左到右），返回一个连续减少值的数组。
使用 Array.prototype.reduce() 将给定函数应用于给定数组，存储每个新结果。
const reduceSuccessive = (arr, fn, acc) =>
arr.reduce((res, val, i, arr) => (res.push(fn(res.slice(-1)[0], val, i, arr)), res), [acc]);
Examples
reduceSuccessive([1, 2, 3, 4, 5, 6], (acc, val) => acc + val, 0); // [0, 1, 3, 6, 10, 15, 21]
reduceWhich
在应用提供的函数设置比较规则后，返回数组的最小值/最大值。
结合使用 Array.prototype.reduce() 和 comparator 函数来获取数组中的适当元素。 您可以省略第二个参数 comparator，以使用返回数组中最小元素的默认参数。
const reduceWhich = (arr, comparator = (a, b) => a - b) =>
arr.reduce((a, b) => (comparator(a, b) >= 0 ? b : a));
Examples
reduceWhich([1, 3, 2]); // 1
reduceWhich([1, 3, 2], (a, b) => b - a); // 3
reduceWhich(
[{ name: 'Tom', age: 12 }, { name: 'Jack', age: 18 }, { name: 'Lucy', age: 9 }],
(a, b) => a.age - b.age
); // {name: "Lucy", age: 9}
reject
采用谓词和数组，如 Array.prototype.filter()，但只保留 x< /code> 如果 pred(x) === false。
const reject = (pred, array) => array.filter((...args) => !pred(...args));
Examples
reject(x => x % 2 === 0, [1, 2, 3, 4, 5]); // [1, 3, 5]
reject(word => word.length > 4, ['Apple', 'Pear', 'Kiwi', 'Banana']); // ['Pear', 'Kiwi']
remove
从给定函数返回 false 的数组中删除元素。
使用 Array.prototype.filter() 查找返回真值的数组元素，使用 Array.prototype.reduce() 使用 Array.prototype.splice 删除元素()。 func 使用三个参数（value、index、array）调用。
const remove = (arr, func) =>
Array.isArray(arr)
? arr.filter(func).reduce((acc, val) => {
arr.splice(arr.indexOf(val), 1);
return acc.concat(val);
}, [])
: [];
Examples
remove([1, 2, 3, 4], n => n % 2 === 0); // [2, 4]
sample
从数组中返回一个随机元素。
使用 Math.random() 生成随机数，将其乘以 length 并使用 Math.floor()。 此方法也适用于字符串。
const sample = arr => arr[Math.floor(Math.random() * arr.length)];
Examples
sample([3, 7, 9, 11]); // 9
sampleSize
从 array 的唯一键处获取 n 个随机元素，最大大小为 数组。
使用 Fisher-Yates 算法 打乱数组。 使用 Array.prototype.slice() 获取第一个 n 元素。 省略第二个参数 n 以仅从数组中随机获取一个元素。
const sampleSize = ([...arr], n = 1) => {
let m = arr.length;
while (m) {
const i = Math.floor(Math.random() * m--);
[arr[m], arr[i]] = [arr[i], arr[m]];
}
return arr.slice(0, n);
};
Examples
sampleSize([1, 2, 3], 2); // [3,1]
sampleSize([1, 2, 3], 4); // [2,3,1]
shank
与 Array.prototype.splice()，但返回一个新数组而不是改变原始数组。
在删除现有元素和/或添加新元素后，使用 Array.prototype.slice() 和 Array.prototype.concat() 获取包含新内容的新数组。 省略第二个参数 index，从 0 开始。 省略第三个参数 delCount，以删除 0 元素。 省略第四个参数 elements，以便不添加任何新元素。
const shank = (arr, index = 0, delCount = 0, ...elements) =>
arr
.slice(0, index)
.concat(elements)
.concat(arr.slice(index + delCount));
Examples
const names = ['alpha', 'bravo', 'charlie'];
const namesAndDelta = shank(names, 1, 0, 'delta'); // [ 'alpha', 'delta', 'bravo', 'charlie' ]
const namesNoBravo = shank(names, 1, 1); // [ 'alpha', 'charlie' ]
console.log(names); // ['alpha', 'bravo', 'charlie']
shuffle
随机化数组值的顺序，返回一个新数组。
使用 Fisher-Yates 算法 对数组元素重新排序。
const shuffle = ([...arr]) => {
let m = arr.length;
while (m) {
const i = Math.floor(Math.random() * m--);
[arr[m], arr[i]] = [arr[i], arr[m]];
}
return arr;
};
Examples
const foo = [1, 2, 3];
shuffle(foo); // [2, 3, 1], foo = [1, 2, 3]
similarity
返回出现在两个数组中的元素数组。
使用 Array.prototype.filter() 删除不属于 values 的值，使用 Array.prototype.includes() 确定。
const similarity = (arr, values) => arr.filter(v => values.includes(v));
Examples
similarity([1, 2, 3], [1, 2, 4]); // [1, 2]
sortedIndex
Returns the lowest index at which value should be inserted into array in order to maintain its sort order.
Check if the array is sorted in descending order (loosely). Use Array.prototype.findIndex() to find the appropriate index where the element should be inserted.
const sortedIndex = (arr, n) => {
const isDescending = arr[0] > arr[arr.length - 1];
const index = arr.findIndex(el => (isDescending ? n >= el : n <= el));
return index === -1 ? arr.length : index;
};
Examples
sortedIndex([5, 3, 2, 1], 4); // 1
sortedIndex([30, 50], 40); // 1
sortedIndexBy
Returns the lowest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.
Check if the array is sorted in descending order (loosely). Use Array.prototype.findIndex() to find the appropriate index where the element should be inserted, based on the iterator function fn.
const sortedIndexBy = (arr, n, fn) => {
const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
const val = fn(n);
const index = arr.findIndex(el => (isDescending ? val >= fn(el) : val <= fn(el)));
return index === -1 ? arr.length : index;
};
Examples
sortedIndexBy([{ x: 4 }, { x: 5 }], { x: 4 }, o => o.x); // 0
sortedLastIndex
Returns the highest index at which value should be inserted into array in order to maintain its sort order.
Check if the array is sorted in descending order (loosely). Use Array.prototype.reverse() and Array.prototype.findIndex() to find the appropriate last index where the element should be inserted.
const sortedLastIndex = (arr, n) => {
const isDescending = arr[0] > arr[arr.length - 1];
const index = arr.reverse().findIndex(el => (isDescending ? n <= el : n >= el));
return index === -1 ? 0 : arr.length - index;
};
Examples
sortedLastIndex([10, 20, 30, 30, 40], 30); // 4
sor
30 seconds of code
Curated collection of useful JavaScript snippets that you can understand in 30 seconds or less.
- Use Ctrl + F or command + F to search for a snippet.
- Contributions welcome, please read the contribution guide.
- Snippets are written in ES6, use the Babel transpiler to ensure backwards-compatibility.
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Package
⚠️ NOTICE: A few of our snippets are not yet optimized for production (see disclaimers for individual snippet issues).
You can find a package with all the snippets on npm.
# With npm
npm install 30-seconds-of-code
# With yarn
yarn add 30-seconds-of-code
Details
Browser
<script src="https://unpkg.com/30-seconds-of-code@1/dist/_30s.es5.min.js"></script>
<script>
_30s.average(1, 2, 3);
</script>
Node
// CommonJS
const _30s = require('30-seconds-of-code');
_30s.average(1, 2, 3);
// ES Modules
import _30s from '30-seconds-of-code';
_30s.average(1, 2, 3);
Contents
???? Adapter
View contents
???? Array
View contents
allallEqualanyarrayToCSVbifurcatebifurcateBychunkcompactcountBycountOccurrencesdeepFlattendifferencedifferenceBydifferenceWithdropdropRightdropRightWhiledropWhileeveryNthfilterNonUniquefilterNonUniqueByfindLastfindLastIndexflattenforEachRightgroupByheadindexOfAllinitialinitialize2DArrayinitializeArrayWithRangeinitializeArrayWithRangeRightinitializeArrayWithValuesinitializeNDArrayintersectionintersectionByintersectionWithisSortedjoinJSONtoCSVlastlongestItemmapObjectmaxNminNnonenthElementoffsetpartitionpermutationspullpullAtIndexpullAtValuepullByreducedFilterreduceSuccessivereduceWhichrejectremovesamplesampleSizeshankshufflesimilaritysortedIndexsortedIndexBysortedLastIndexsortedLastIndexBystableSortsymmetricDifferencesymmetricDifferenceBysymmetricDifferenceWithtailtaketakeRighttakeRightWhiletakeWhiletoHashunionunionByunionWithuniqueElementsuniqueElementsByuniqueElementsByRightuniqueSymmetricDifferenceunzipunzipWithwithoutxProdzipzipObjectzipWith
???? Browser
View contents
arrayToHtmlListbottomVisiblecopyToClipboardcountercreateElementcreateEventHubcurrentURLdetectDeviceTypeelementContainselementIsVisibleInViewportgetImagesgetScrollPositiongetStylehasClasshashBrowserhidehttpsRedirectinsertAfterinsertBeforeisBrowserTabFocusednodeListToArrayobserveMutationsoffononUserInputChangeprefixrecordAnimationFramesredirectrunAsyncscrollToTopsetStyleshowsmoothScrolltoggleClasstriggerEventUUIDGeneratorBrowser
⏱️ Date
View contents
????️ Function
View contents
➗ Math
View contents
approximatelyEqualaverageaverageBybinomialCoefficientclampNumberdegreesToRadsdigitizedistanceelofactorialfibonaccigcdgeometricProgressionhammingDistanceinRangeisDivisibleisEvenisNegativeZeroisPrimelcmluhnCheckmaxBymedianminBypercentilepowersetprimesradsToDegreesrandomIntArrayInRangerandomIntegerInRangerandomNumberInRangeroundsdbmstandardDeviationsumsumBysumPowertoSafeInteger
???? Node
View contents
????️ Object
View contents
???? String
View contents
byteSizecapitalizecapitalizeEveryWordCSVToArrayCSVToJSONdecapitalizeescapeHTMLescapeRegExpfromCamelCaseindentStringisAbsoluteURLisAnagramisLowerCaseisUpperCasemapStringmaskpadpalindromepluralizeremoveNonASCIIreverseStringsortCharactersInStringsplitLinesstringPermutationsstripHTMLTagstoCamelCasetoKebabCasetoSnakeCasetoTitleCasetruncateStringunescapeHTMLURLJoinwords
???? Type
View contents
???? Utility
View contents
???? Adapter
ary
Creates a function that accepts up to n arguments, ignoring any additional arguments.
Call the provided function, fn, with up to n arguments, using Array.prototype.slice(0,n) and the spread operator (...).
const ary = (fn, n) => (...args) => fn(...args.slice(0, n));
Examples
const firstTwoMax = ary(Math.max, 2);
[[2, 6, 'a'], [8, 4, 6], [10]].map(x => firstTwoMax(...x)); // [6, 8, 10]
call
Given a key and a set of arguments, call them when given a context. Primarily useful in composition.
Use a closure to call a stored key with stored arguments.
const call = (key, ...args) => context => context[key](...args);
Examples
Promise.resolve([1, 2, 3])
.then(call('map', x => 2 * x))
.then(console.log); // [ 2, 4, 6 ]
const map = call.bind(null, 'map');
Promise.resolve([1, 2, 3])
.then(map(x => 2 * x))
.then(console.log); // [ 2, 4, 6 ]
collectInto
Changes a function that accepts an array into a variadic function.
Given a function, return a closure that collects all inputs into an array-accepting function.
const collectInto = fn => (...args) => fn(args);
Examples
const Pall = collectInto(Promise.all.bind(Promise));
let p1 = Promise.resolve(1);
let p2 = Promise.resolve(2);
let p3 = new Promise(resolve => setTimeout(resolve, 2000, 3));
Pall(p1, p2, p3).then(console.log); // [1, 2, 3] (after about 2 seconds)
flip
Flip takes a function as an argument, then makes the first argument the last.
Return a closure that takes variadic inputs, and splices the last argument to make it the first argument before applying the rest.
const flip = fn => (first, ...rest) => fn(...rest, first);
Examples
let a = { name: 'John Smith' };
let b = {};
const mergeFrom = flip(Object.assign);
let mergePerson = mergeFrom.bind(null, a);
mergePerson(b); // == b
b = {};
Object.assign(b, a); // == b
over
Creates a function that invokes each provided function with the arguments it receives and returns the results.
Use Array.prototype.map() and Function.prototype.apply() to apply each function to the given arguments.
const over = (...fns) => (...args) => fns.map(fn => fn.apply(null, args));
Examples
const minMax = over(Math.min, Math.max);
minMax(1, 2, 3, 4, 5); // [1,5]
overArgs
Creates a function that invokes the provided function with its arguments transformed.
Use Array.prototype.map() to apply transforms to args in combination with the spread operator (...) to pass the transformed arguments to fn.
const overArgs = (fn, transforms) => (...args) => fn(...args.map((val, i) => transforms[i](val)));
Examples
const square = n => n * n;
const double = n => n * 2;
const fn = overArgs((x, y) => [x, y], [square, double]);
fn(9, 3); // [81, 6]
pipeAsyncFunctions
Performs left-to-right function composition for asynchronous functions.
Use Array.prototype.reduce() with the spread operator (...) to perform left-to-right function composition using Promise.then(). The functions can return a combination of: simple values, Promise's, or they can be defined as async ones returning through await. All functions must be unary.
const pipeAsyncFunctions = (...fns) => arg => fns.reduce((p, f) => p.then(f), Promise.resolve(arg));
Examples
const sum = pipeAsyncFunctions(
x => x + 1,
x => new Promise(resolve => setTimeout(() => resolve(x + 2), 1000)),
x => x + 3,
async x => (await x) + 4
);
(async() => {
console.log(await sum(5)); // 15 (after one second)
})();
pipeFunctions
Performs left-to-right function composition.
Use Array.prototype.reduce() with the spread operator (...) to perform left-to-right function composition. The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
const pipeFunctions = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));
Examples
const add5 = x => x + 5;
const multiply = (x, y) => x * y;
const multiplyAndAdd5 = pipeFunctions(multiply, add5);
multiplyAndAdd5(5, 2); // 15
promisify
Converts an asynchronous function to return a promise.
Use currying to return a function returning a Promise that calls the original function. Use the ...rest operator to pass in all the parameters.
In Node 8+, you can use util.promisify
const promisify = func => (...args) =>
new Promise((resolve, reject) =>
func(...args, (err, result) => (err ? reject(err) : resolve(result)))
);
Examples
const delay = promisify((d, cb) => setTimeout(cb, d));
delay(2000).then(() => console.log('Hi!')); // // Promise resolves after 2s
rearg
Creates a function that invokes the provided function with its arguments arranged according to the specified indexes.
Use Array.prototype.map() to reorder arguments based on indexes in combination with the spread operator (...) to pass the transformed arguments to fn.
const rearg = (fn, indexes) => (...args) => fn(...indexes.map(i => args[i]));
Examples
var rearged = rearg(
function(a, b, c) {
return [a, b, c];
},
[2, 0, 1]
);
rearged('b', 'c', 'a'); // ['a', 'b', 'c']
spreadOver
Takes a variadic function and returns a closure that accepts an array of arguments to map to the inputs of the function.
Use closures and the spread operator (...) to map the array of arguments to the inputs of the function.
const spreadOver = fn => argsArr => fn(...argsArr);
Examples
const arrayMax = spreadOver(Math.max);
arrayMax([1, 2, 3]); // 3
unary
Creates a function that accepts up to one argument, ignoring any additional arguments.
Call the provided function, fn, with just the first argument given.
const unary = fn => val => fn(val);
Examples
['6', '8', '10'].map(unary(parseInt)); // [6, 8, 10]
???? Array
all
Returns true if the provided predicate function returns true for all elements in a collection, false otherwise.
Use Array.prototype.every() to test if all elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.
const all = (arr, fn = Boolean) => arr.every(fn);
Examples
all([4, 2, 3], x => x > 1); // true
all([1, 2, 3]); // true
allEqual
Check if all elements in an array are equal.
Use Array.prototype.every() to check if all the elements of the array are the same as the first one.
const allEqual = arr => arr.every(val => val === arr[0]);
Examples
allEqual([1, 2, 3, 4, 5, 6]); // false
allEqual([1, 1, 1, 1]); // true
any
Returns true if the provided predicate function returns true for at least one element in a collection, false otherwise.
Use Array.prototype.some() to test if any elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.
const any = (arr, fn = Boolean) => arr.some(fn);
Examples
any([0, 1, 2, 0], x => x >= 2); // true
any([0, 0, 1, 0]); // true
arrayToCSV
Converts a 2D array to a comma-separated values (CSV) string.
Use Array.prototype.map() and Array.prototype.join(delimiter) to combine individual 1D arrays (rows) into strings. Use Array.prototype.join('\n') to combine all rows into a CSV string, separating each row with a newline. Omit the second argument, delimiter, to use a default delimiter of ,.
const arrayToCSV = (arr, delimiter = ',') =>
arr.map(v => v.map(x => `"${x}"`).join(delimiter)).join('\n');
Examples
arrayToCSV([['a', 'b'], ['c', 'd']]); // '"a","b"\n"c","d"'
arrayToCSV([['a', 'b'], ['c', 'd']], ';'); // '"a";"b"\n"c";"d"'
bifurcate
Splits values into two groups. If an element in filter is truthy, the corresponding element in the collection belongs to the first group; otherwise, it belongs to the second group.
Use Array.prototype.reduce() and Array.prototype.push() to add elements to groups, based on filter.
const bifurcate = (arr, filter) =>
arr.reduce((acc, val, i) => (acc[filter[i] ? 0 : 1].push(val), acc), [[], []]);
Examples
bifurcate(['beep', 'boop', 'foo', 'bar'], [true, true, false, true]); // [ ['beep', 'boop', 'bar'], ['foo'] ]
bifurcateBy
Splits values into two groups according to a predicate function, which specifies which group an element in the input collection belongs to. If the predicate function returns a truthy value, the collection element belongs to the first group; otherwise, it belongs to the second group.
Use Array.prototype.reduce() and Array.prototype.push() to add elements to groups, based on the value returned by fn for each element.
const bifurcateBy = (arr, fn) =>
arr.reduce((acc, val, i) => (acc[fn(val, i) ? 0 : 1].push(val), acc), [[], []]);
Examples
bifurcateBy(['beep', 'boop', 'foo', 'bar'], x => x[0] === 'b'); // [ ['beep', 'boop', 'bar'], ['foo'] ]
chunk
Chunks an array into smaller arrays of a specified size.
Use Array.from() to create a new array, that fits the number of chunks that will be produced. Use Array.prototype.slice() to map each element of the new array to a chunk the length of size. If the original array can't be split evenly, the final chunk will contain the remaining elements.
const chunk = (arr, size) =>
Array.from({ length: Math.ceil(arr.length / size) }, (v, i) =>
arr.slice(i * size, i * size + size)
);
Examples
chunk([1, 2, 3, 4, 5], 2); // [[1,2],[3,4],[5]]
compact
Removes falsey values from an array.
Use Array.prototype.filter() to filter out falsey values (false, null, 0, "", undefined, and NaN).
const compact = arr => arr.filter(Boolean);
Examples
compact([0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34]); // [ 1, 2, 3, 'a', 's', 34 ]
countBy
Groups the elements of an array based on the given function and returns the count of elements in each group.
Use Array.prototype.map() to map the values of an array to a function or property name. Use Array.prototype.reduce() to create an object, where the keys are produced from the mapped results.
const countBy = (arr, fn) =>
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => {
acc[val] = (acc[val] || 0) + 1;
return acc;
}, {});
Examples
countBy([6.1, 4.2, 6.3], Math.floor); // {4: 1, 6: 2}
countBy(['one', 'two', 'three'], 'length'); // {3: 2, 5: 1}
countOccurrences
Counts the occurrences of a value in an array.
Use Array.prototype.reduce() to increment a counter each time you encounter the specific value inside the array.
const countOccurrences = (arr, val) => arr.reduce((a, v) => (v === val ? a + 1 : a), 0);
Examples
countOccurrences([1, 1, 2, 1, 2, 3], 1); // 3
deepFlatten
Deep flattens an array.
Use recursion. Use Array.prototype.concat() with an empty array ([]) and the spread operator (...) to flatten an array. Recursively flatten each element that is an array.
const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));
Examples
deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5]
difference
Returns the difference between two arrays.
Create a Set from b, then use Array.prototype.filter() on a to only keep values not contained in b.
const difference = (a, b) => {
const s = new Set(b);
return a.filter(x => !s.has(x));
};
Examples
difference([1, 2, 3], [1, 2, 4]); // [3]
differenceBy
Returns the difference between two arrays, after applying the provided function to each array element of both.
Create a Set by applying fn to each element in b, then use Array.prototype.filter() in combination with fn on a to only keep values not contained in the previously created set.
const differenceBy = (a, b, fn) => {
const s = new Set(b.map(fn));
return a.filter(x => !s.has(fn(x)));
};
Examples
differenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [1.2]
differenceBy([{ x: 2 }, { x: 1 }], [{ x: 1 }], v => v.x); // [ { x: 2 } ]
differenceWith
Filters out all values from an array for which the comparator function does not return true.
Use Array.prototype.filter() and Array.prototype.findIndex() to find the appropriate values.
const differenceWith = (arr, val, comp) => arr.filter(a => val.findIndex(b => comp(a, b)) === -1);
Examples
differenceWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0], (a, b) => Math.round(a) === Math.round(b)); // [1, 1.2]
drop
Returns a new array with n elements removed from the left.
Use Array.prototype.slice() to slice the remove the specified number of elements from the left.
const drop = (arr, n = 1) => arr.slice(n);
Examples
drop([1, 2, 3]); // [2,3]
drop([1, 2, 3], 2); // [3]
drop([1, 2, 3], 42); // []
dropRight
Returns a new array with n elements removed from the right.
Use Array.prototype.slice() to slice the remove the specified number of elements from the right.
const dropRight = (arr, n = 1) => arr.slice(0, -n);
Examples
dropRight([1, 2, 3]); // [1,2]
dropRight([1, 2, 3], 2); // [1]
dropRight([1, 2, 3], 42); // []
dropRightWhile
Removes elements from the end of an array until the passed function returns true. Returns the remaining elements in the array.
Loop through the array, using Array.prototype.slice() to drop the last element of the array until the returned value from the function is true. Returns the remaining elements.
const dropRightWhile = (arr, func) => {
while (arr.length > 0 && !func(arr[arr.length - 1])) arr = arr.slice(0, -1);
return arr;
};
Examples
dropRightWhile([1, 2, 3, 4], n => n < 3); // [1, 2]
dropWhile
Removes elements in an array until the passed function returns true. Returns the remaining elements in the array.
Loop through the array, using Array.prototype.slice() to drop the first element of the array until the returned value from the function is true. Returns the remaining elements.
const dropWhile = (arr, func) => {
while (arr.length > 0 && !func(arr[0])) arr = arr.slice(1);
return arr;
};
Examples
dropWhile([1, 2, 3, 4], n => n >= 3); // [3,4]
everyNth
Returns every nth element in an array.
Use Array.prototype.filter() to create a new array that contains every nth element of a given array.
const everyNth = (arr, nth) => arr.filter((e, i) => i % nth === nth - 1);
Examples
everyNth([1, 2, 3, 4, 5, 6], 2); // [ 2, 4, 6 ]
filterNonUnique
Filters out the non-unique values in an array.
Use Array.prototype.filter() for an array containing only the unique values.
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
Examples
filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1, 3, 5]
filterNonUniqueBy
Filters out the non-unique values in an array, based on a provided comparator function.
Use Array.prototype.filter() and Array.prototype.every() for an array containing only the unique values, based on the comparator function, fn. The comparator function takes four arguments: the values of the two elements being compared and their indexes.
const filterNonUniqueBy = (arr, fn) =>
arr.filter((v, i) => arr.every((x, j) => (i === j) === fn(v, x, i, j)));
Examples
filterNonUniqueBy(
[
{ id: 0, value: 'a' },
{ id: 1, value: 'b' },
{ id: 2, value: 'c' },
{ id: 1, value: 'd' },
{ id: 0, value: 'e' }
],
(a, b) => a.id == b.id
); // [ { id: 2, value: 'c' } ]
findLast
Returns the last element for which the provided function returns a truthy value.
Use Array.prototype.filter() to remove elements for which fn returns falsey values, Array.prototype.pop() to get the last one.
const findLast = (arr, fn) => arr.filter(fn).pop();
Examples
findLast([1, 2, 3, 4], n => n % 2 === 1); // 3
findLastIndex
Returns the index of the last element for which the provided function returns a truthy value.
Use Array.prototype.map() to map each element to an array with its index and value. Use Array.prototype.filter() to remove elements for which fn returns falsey values, Array.prototype.pop() to get the last one.
const findLastIndex = (arr, fn) =>
arr
.map((val, i) => [i, val])
.filter(([i, val]) => fn(val, i, arr))
.pop()[0];
Examples
findLastIndex([1, 2, 3, 4], n => n % 2 === 1); // 2 (index of the value 3)
flatten
Flattens an array up to the specified depth.
Use recursion, decrementing depth by 1 for each level of depth. Use Array.prototype.reduce() and Array.prototype.concat() to merge elements or arrays. Base case, for depth equal to 1 stops recursion. Omit the second argument, depth to flatten only to a depth of 1 (single flatten).
const flatten = (arr, depth = 1) =>
arr.reduce((a, v) => a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v), []);
Examples
flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]
forEachRight
Executes a provided function once for each array element, starting from the array's last element.
Use Array.prototype.slice(0) to clone the given array, Array.prototype.reverse() to reverse it and Array.prototype.forEach() to iterate over the reversed array.
const forEachRight = (arr, callback) =>
arr
.slice(0)
.reverse()
.forEach(callback);
Examples
forEachRight([1, 2, 3, 4], val => console.log(val)); // '4', '3', '2', '1'
groupBy
Groups the elements of an array based on the given function.
Use Array.prototype.map() to map the values of an array to a function or property name. Use Array.prototype.reduce() to create an object, where the keys are produced from the mapped results.
const groupBy = (arr, fn) =>
arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val, i) => {
acc[val] = (acc[val] || []).concat(arr[i]);
return acc;
}, {});
Examples
groupBy([6.1, 4.2, 6.3], Math.floor); // {4: [4.2], 6: [6.1, 6.3]}
groupBy(['one', 'two', 'three'], 'length'); // {3: ['one', 'two'], 5: ['three']}
head
Returns the head of a list.
Use arr[0] to return the first element of the passed array.
const head = arr => arr[0];
Examples
head([1, 2, 3]); // 1
indexOfAll
Returns all indices of val in an array. If val never occurs, returns [].
Use Array.prototype.reduce() to loop over elements and store indices for matching elements. Return the array of indices.
const indexOfAll = (arr, val) => arr.reduce((acc, el, i) => (el === val ? [...acc, i] : acc), []);
Examples
indexOfAll([1, 2, 3, 1, 2, 3], 1); // [0,3]
indexOfAll([1, 2, 3], 4); // []
initial
Returns all the elements of an array except the last one.
Use arr.slice(0,-1) to return all but the last element of the array.
const initial = arr => arr.slice(0, -1);
Examples
initial([1, 2, 3]); // [1,2]
initialize2DArray
Initializes a 2D array of given width and height and value.
Use Array.prototype.map() to generate h rows where each is a new array of size w initialize with value. If the value is not provided, default to null.
const initialize2DArray = (w, h, val = null) =>
Array.from({ length: h }).map(() => Array.from({ length: w }).fill(val));
Examples
initialize2DArray(2, 2, 0); // [[0,0], [0,0]]
initializeArrayWithRange
Initializes an array containing the numbers in the specified range where start and end are inclusive with their common difference step.
Use Array.from() to create an array of the desired length, (end - start + 1)/step, and a map function to fill it with the desired values in the given range. You can omit start to use a default value of 0. You can omit step to use a default value of 1.
const initializeArrayWithRange = (end, start = 0, step = 1) =>
Array.from({ length: Math.ceil((end - start + 1) / step) }, (v, i) => i * step + start);
Examples
initializeArrayWithRange(5); // [0,1,2,3,4,5]
initializeArrayWithRange(7, 3); // [3,4,5,6,7]
initializeArrayWithRange(9, 0, 2); // [0,2,4,6,8]
initializeArrayWithRangeRight
Initializes an array containing the numbers in the specified range (in reverse) where start and end are inclusive with their common difference step.
Use Array.from(Math.ceil((end+1-start)/step)) to create an array of the desired length(the amounts of elements is equal to (end-start)/step or (end+1-start)/step for inclusive end), Array.prototype.map() to fill with the desired values in a range. You can omit start to use a default value of 0. You can omit step to use a default value of 1.
const initializeArrayWithRangeRight = (end, start = 0, step = 1) =>
Array.from({ length: Math.ceil((end + 1 - start) / step) }).map(
(v, i, arr) => (arr.length - i - 1) * step + start
);
Examples
initializeArrayWithRangeRight(5); // [5,4,3,2,1,0]
initializeArrayWithRangeRight(7, 3); // [7,6,5,4,3]
initializeArrayWithRangeRight(9, 0, 2); // [8,6,4,2,0]
initializeArrayWithValues
Initializes and fills an array with the specified values.
Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values. You can omit val to use a default value of 0.
const initializeArrayWithValues = (n, val = 0) => Array(n).fill(val);
Examples
initializeArrayWithValues(5, 2); // [2, 2, 2, 2, 2]
initializeNDArray
Create a n-dimensional array with given value.
Use recursion. Use Array.prototype.map() to generate rows where each is a new array initialized using initializeNDArray.
const initializeNDArray = (val, ...args) =>
args.length === 0
? val
: Array.from({ length: args[0] }).map(() => initializeNDArray(val, ...args.slice(1)));
Examples
initializeNDArray(1, 3); // [1,1,1]
initializeNDArray(5, 2, 2, 2); // [[[5,5],[5,5]],[[5,5],[5,5]]]
intersection
Returns a list of elements that exist in both arrays.
Create a Set from b, then use Array.prototype.filter() on a to only keep values contained in b.
const intersection = (a, b) => {
const s = new Set(b);
return a.filter(x => s.has(x));
};
Examples
intersection([1, 2, 3], [4, 3, 2]); // [2, 3]
intersectionBy
Returns a list of elements that exist in both arrays, after applying the provided function to each array element of both.
Create a Set by applying fn to all elements in b, then use Array.prototype.filter() on a to only keep elements, which produce values contained in b when fn is applied to them.
const intersectionBy = (a, b, fn) => {
const s = new Set(b.map(fn));
return a.filter(x => s.has(fn(x)));
};
Examples
intersectionBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [2.1]
intersectionWith
Returns a list of elements that exist in both arrays, using a provided comparator function.
Use Array.prototype.filter() and Array.prototype.findIndex() in combination with the provided comparator to determine intersecting values.
const intersectionWith = (a, b, comp) => a.filter(x => b.findIndex(y => comp(x, y)) !== -1);
Examples
intersectionWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b)); // [1.5, 3, 0]
isSorted
Returns 1 if the array is sorted in ascending order, -1 if it is sorted in descending order or 0 if it is not sorted.
Calculate the ordering direction for the first two elements. Use Object.entries() to loop over array objects and compare them in pairs. Return 0 if the direction changes or the direction if the last element is reached.
const isSorted = arr => {
let direction = -(arr[0] - arr[1]);
for (let [i, val] of arr.entries()) {
direction = !direction ? -(arr[i - 1] - arr[i]) : direction;
if (i === arr.length - 1) return !direction ? 0 : direction;
else if ((val - arr[i + 1]) * direction > 0) return 0;
}
};
Examples
isSorted([0, 1, 2, 2]); // 1
isSorted([4, 3, 2]); // -1
isSorted([4, 3, 5]); // 0
join
Joins all elements of an array into a string and returns this string. Uses a separator and an end separator.
Use Array.prototype.reduce() to combine elements into a string. Omit the second argument, separator, to use a default separator of ','. Omit the third argument, end, to use the same value as separator by default.
const join = (arr, separator = ',', end = separator) =>
arr.reduce(
(acc, val, i) =>
i === arr.length - 2
? acc + val + end
: i === arr.length - 1
? acc + val
: acc + val + separator,
''
);
Examples
join(['pen', 'pineapple', 'apple', 'pen'], ',', '&'); // "pen,pineapple,apple&pen"
join(['pen', 'pineapple', 'apple', 'pen'], ','); // "pen,pineapple,apple,pen"
join(['pen', 'pineapple', 'apple', 'pen']); // "pen,pineapple,apple,pen"
JSONtoCSV
Converts an array of objects to a comma-separated values (CSV) string that contains only the columns specified.
Use Array.prototype.join(delimiter) to combine all the names in columns to create the first row. Use Array.prototype.map() and Array.prototype.reduce() to create a row for each object, substituting non-existent values with empty strings and only mapping values in columns. Use Array.prototype.join('\n') to combine all rows into a string. Omit the third argument, delimiter, to use a default delimiter of ,.
const JSONtoCSV = (arr, columns, delimiter = ',') =>
[
columns.join(delimiter),
...arr.map(obj =>
columns.reduce(
(acc, key) => `${acc}${!acc.length ? '' : delimiter}"${!obj[key] ? '' : obj[key]}"`,
''
)
)
].join('\n');
Examples
JSONtoCSV([{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }], ['a', 'b']); // 'a,b\n"1","2"\n"3","4"\n"6",""\n"","7"'
JSONtoCSV([{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }], ['a', 'b'], ';'); // 'a;b\n"1";"2"\n"3";"4"\n"6";""\n"";"7"'
last
Returns the last element in an array.
Use arr.length - 1 to compute the index of the last element of the given array and returning it.
const last = arr => arr[arr.length - 1];
Examples
last([1, 2, 3]); // 3
longestItem
Takes any number of iterable objects or objects with a length property and returns the longest one. If multiple objects have the same length, the first one will be returned. Returns undefined if no arguments are provided.
Use Array.prototype.reduce(), comparing the length of objects to find the longest one.
const longestItem = (...vals) => vals.reduce((a, x) => (x.length > a.length ? x : a));
Examples
longestItem('this', 'is', 'a', 'testcase'); // 'testcase'
longestItem(...['a', 'ab', 'abc']); // 'abc'
longestItem(...['a', 'ab', 'abc'], 'abcd'); // 'abcd'
longestItem([1, 2, 3], [1, 2], [1, 2, 3, 4, 5]); // [1, 2, 3, 4, 5]
longestItem([1, 2, 3], 'foobar'); // 'foobar'
mapObject
Maps the values of an array to an object using a function, where the key-value pairs consist of the original value as the key and the mapped value.
Use an anonymous inner function scope to declare an undefined memory space, using closures to store a return value. Use a new Array to store the array with a map of the function over its data set and a comma operator to return a second step, without needing to move from one context to another (due to closures and order of operations).
const mapObject = (arr, fn) =>
(a => (
(a = [arr, arr.map(fn)]), a[0].reduce((acc, val, ind) => ((acc[val] = a[1][ind]), acc), {})
))();
Examples
const squareIt = arr => mapObject(arr, a => a * a);
squareIt([1, 2, 3]); // { 1: 1, 2: 4, 3: 9 }
maxN
Returns the n maximum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array (sorted in descending order).
Use Array.prototype.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in descending order. Use Array.prototype.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n);
Examples
maxN([1, 2, 3]); // [3]
maxN([1, 2, 3], 2); // [3,2]
minN
Returns the n minimum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array (sorted in ascending order).
Use Array.prototype.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in ascending order. Use Array.prototype.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
const minN = (arr, n = 1) => [...arr].sort((a, b) => a - b).slice(0, n);
Examples
minN([1, 2, 3]); // [1]
minN([1, 2, 3], 2); // [1,2]
none
Returns true if the provided predicate function returns false for all elements in a collection, false otherwise.
Use Array.prototype.some() to test if any elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.
const none = (arr, fn = Boolean) => !arr.some(fn);
Examples
none([0, 1, 3, 0], x => x == 2); // true
none([0, 0, 0]); // true
nthElement
Returns the nth element of an array.
Use Array.prototype.slice() to get an array containing the nth element at the first place. If the index is out of bounds, return undefined. Omit the second argument, n, to get the first element of the array.
const nthElement = (arr, n = 0) => (n === -1 ? arr.slice(n) : arr.slice(n, n + 1))[0];
Examples
nthElement(['a', 'b', 'c'], 1); // 'b'
nthElement(['a', 'b', 'b'], -3); // 'a'
offset
Moves the specified amount of elements to the end of the array.
Use Array.prototype.slice() twice to get the elements after the specified index and the elements before that. Use the spread operator(...) to combine the two into one array. If offset is negative, the elements will be moved from end to start.
const offset = (arr, offset) => [...arr.slice(offset), ...arr.slice(0, offset)];
Examples
offset([1, 2, 3, 4, 5], 2); // [3, 4, 5, 1, 2]
offset([1, 2, 3, 4, 5], -2); // [4, 5, 1, 2, 3]
partition
Groups the elements into two arrays, depending on the provided function's truthiness for each element.
Use Array.prototype.reduce() to create an array of two arrays. Use Array.prototype.push() to add elements for which fn returns true to the first array and elements for which fn returns false to the second one.
const partition = (arr, fn) =>
arr.reduce(
(acc, val, i, arr) => {
acc[fn(val, i, arr) ? 0 : 1].push(val);
return acc;
},
[[], []]
);
Examples
const users = [{ user: 'barney', age: 36, active: false }, { user: 'fred', age: 40, active: true }];
partition(users, o => o.active); // [[{ 'user': 'fred', 'age': 40, 'active': true }],[{ 'user': 'barney', 'age': 36, 'active': false }]]
permutations
⚠️ WARNING: This function's execution time increases exponentially with each array element. Anything more than 8 to 10 entries will cause your browser to hang as it tries to solve all the different combinations.
Generates all permutations of an array's elements (contains duplicates).
Use recursion. For each element in the given array, create all the partial permutations for the rest of its elements. Use Array.prototype.map() to combine the element with each partial permutation, then Array.prototype.reduce() to combine all permutations in one array. Base cases are for array length equal to 2 or 1.
const permutations = arr => {
if (arr.length <= 2) return arr.length === 2 ? [arr, [arr[1], arr[0]]] : arr;
return arr.reduce(
(acc, item, i) =>
acc.concat(
permutations([...arr.slice(0, i), ...arr.slice(i + 1)]).map(val => [item, ...val])
),
[]
);
};
Examples
permutations([1, 33, 5]); // [ [ 1, 33, 5 ], [ 1, 5, 33 ], [ 33, 1, 5 ], [ 33, 5, 1 ], [ 5, 1, 33 ], [ 5, 33, 1 ] ]
pull
Mutates the original array to filter out the values specified.
Use Array.prototype.filter() and Array.prototype.includes() to pull out the values that are not needed. Use Array.prototype.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.prototype.push() to re-populate it with only the pulled values.
(For a snippet that does not mutate the original array see without)
const pull = (arr, ...args) => {
let argState = Array.isArray(args[0]) ? args[0] : args;
let pulled = arr.filter((v, i) => !argState.includes(v));
arr.length = 0;
pulled.forEach(v => arr.push(v));
};
Examples
let myArray = ['a', 'b', 'c', 'a', 'b', 'c'];
pull(myArray, 'a', 'c'); // myArray = [ 'b', 'b' ]
pullAtIndex
Mutates the original array to filter out the values at the specified indexes.
Use Array.prototype.filter() and Array.prototype.includes() to pull out the values that are not needed. Use Array.prototype.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.prototype.push() to re-populate it with only the pulled values. Use Array.prototype.push() to keep track of pulled values
const pullAtIndex = (arr, pullArr) => {
let removed = [];
let pulled = arr
.map((v, i) => (pullArr.includes(i) ? removed.push(v) : v))
.filter((v, i) => !pullArr.includes(i));
arr.length = 0;
pulled.forEach(v => arr.push(v));
return removed;
};
Examples
let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtIndex(myArray, [1, 3]); // myArray = [ 'a', 'c' ] , pulled = [ 'b', 'd' ]
pullAtValue
Mutates the original array to filter out the values specified. Returns the removed elements.
Use Array.prototype.filter() and Array.prototype.includes() to pull out the values that are not needed. Use Array.prototype.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.prototype.push() to re-populate it with only the pulled values. Use Array.prototype.push() to keep track of pulled values
const pullAtValue = (arr, pullArr) => {
let removed = [],
pushToRemove = arr.forEach((v, i) => (pullArr.includes(v) ? removed.push(v) : v)),
mutateTo = arr.filter((v, i) => !pullArr.includes(v));
arr.length = 0;
mutateTo.forEach(v => arr.push(v));
return removed;
};
Examples
let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtValue(myArray, ['b', 'd']); // myArray = [ 'a', 'c' ] , pulled = [ 'b', 'd' ]
pullBy
Mutates the original array to filter out the values specified, based on a given iterator function.
Check if the last argument provided in a function. Use Array.prototype.map() to apply the iterator function fn to all array elements. Use Array.prototype.filter() and Array.prototype.includes() to pull out the values that are not needed. Use Array.prototype.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.prototype.push() to re-populate it with only the pulled values.
const pullBy = (arr, ...args) => {
const length = args.length;
let fn = length > 1 ? args[length - 1] : undefined;
fn = typeof fn == 'function' ? (args.pop(), fn) : undefined;
let argState = (Array.isArray(args[0]) ? args[0] : args).map(val => fn(val));
let pulled = arr.filter((v, i) => !argState.includes(fn(v)));
arr.length = 0;
pulled.forEach(v => arr.push(v));
};
Examples
var myArray = [{ x: 1 }, { x: 2 }, { x: 3 }, { x: 1 }];
pullBy(myArray, [{ x: 1 }, { x: 3 }], o => o.x); // myArray = [{ x: 2 }]
reducedFilter
Filter an array of objects based on a condition while also filtering out unspecified keys.
Use Array.prototype.filter() to filter the array based on the predicate fn so that it returns the objects for which the condition returned a truthy value. On the filtered array, use Array.prototype.map() to return the new object using Array.prototype.reduce() to filter out the keys which were not supplied as the keys argument.
const reducedFilter = (data, keys, fn) =>
data.filter(fn).map(el =>
keys.reduce((acc, key) => {
acc[key] = el[key];
return acc;
}, {})
);
Examples
const data = [
{
id: 1,
name: 'john',
age: 24
},
{
id: 2,
name: 'mike',
age: 50
}
];
reducedFilter(data, ['id', 'name'], item => item.age > 24); // [{ id: 2, name: 'mike'}]
reduceSuccessive
Applies a function against an accumulator and each element in the array (from left to right), returning an array of successively reduced values.
Use Array.prototype.reduce() to apply the given function to the given array, storing each new result.
const reduceSuccessive = (arr, fn, acc) =>
arr.reduce((res, val, i, arr) => (res.push(fn(res.slice(-1)[0], val, i, arr)), res), [acc]);
Examples
reduceSuccessive([1, 2, 3, 4, 5, 6], (acc, val) => acc + val, 0); // [0, 1, 3, 6, 10, 15, 21]
reduceWhich
Returns the minimum/maximum value of an array, after applying the provided function to set comparing rule.
Use Array.prototype.reduce() in combination with the comparator function to get the appropriate element in the array. You can omit the second parameter, comparator, to use the default one that returns the minimum element in the array.
const reduceWhich = (arr, comparator = (a, b) => a - b) =>
arr.reduce((a, b) => (comparator(a, b) >= 0 ? b : a));
Examples
reduceWhich([1, 3, 2]); // 1
reduceWhich([1, 3, 2], (a, b) => b - a); // 3
reduceWhich(
[{ name: 'Tom', age: 12 }, { name: 'Jack', age: 18 }, { name: 'Lucy', age: 9 }],
(a, b) => a.age - b.age
); // {name: "Lucy", age: 9}
reject
Takes a predicate and array, like Array.prototype.filter(), but only keeps x if pred(x) === false.
const reject = (pred, array) => array.filter((...args) => !pred(...args));
Examples
reject(x => x % 2 === 0, [1, 2, 3, 4, 5]); // [1, 3, 5]
reject(word => word.length > 4, ['Apple', 'Pear', 'Kiwi', 'Banana']); // ['Pear', 'Kiwi']
remove
Removes elements from an array for which the given function returns false.
Use Array.prototype.filter() to find array elements that return truthy values and Array.prototype.reduce() to remove elements using Array.prototype.splice(). The func is invoked with three arguments (value, index, array).
const remove = (arr, func) =>
Array.isArray(arr)
? arr.filter(func).reduce((acc, val) => {
arr.splice(arr.indexOf(val), 1);
return acc.concat(val);
}, [])
: [];
Examples
remove([1, 2, 3, 4], n => n % 2 === 0); // [2, 4]
sample
Returns a random element from an array.
Use Math.random() to generate a random number, multiply it by length and round it off to the nearest whole number using Math.floor(). This method also works with strings.
const sample = arr => arr[Math.floor(Math.random() * arr.length)];
Examples
sample([3, 7, 9, 11]); // 9
sampleSize
Gets n random elements at unique keys from array up to the size of array.
Shuffle the array using the Fisher-Yates algorithm. Use Array.prototype.slice() to get the first n elements. Omit the second argument, n to get only one element at random from the array.
const sampleSize = ([...arr], n = 1) => {
let m = arr.length;
while (m) {
const i = Math.floor(Math.random() * m--);
[arr[m], arr[i]] = [arr[i], arr[m]];
}
return arr.slice(0, n);
};
Examples
sampleSize([1, 2, 3], 2); // [3,1]
sampleSize([1, 2, 3], 4); // [2,3,1]
shank
Has the same functionality as Array.prototype.splice(), but returning a new array instead of mutating the original array.
Use Array.prototype.slice() and Array.prototype.concat() to get a new array with the new contents after removing existing elements and/or adding new elements. Omit the second argument, index, to start at 0. Omit the third argument, delCount, to remove 0 elements. Omit the fourth argument, elements, in order to not add any new elements.
const shank = (arr, index = 0, delCount = 0, ...elements) =>
arr
.slice(0, index)
.concat(elements)
.concat(arr.slice(index + delCount));
Examples
const names = ['alpha', 'bravo', 'charlie'];
const namesAndDelta = shank(names, 1, 0, 'delta'); // [ 'alpha', 'delta', 'bravo', 'charlie' ]
const namesNoBravo = shank(names, 1, 1); // [ 'alpha', 'charlie' ]
console.log(names); // ['alpha', 'bravo', 'charlie']
shuffle
Randomizes the order of the values of an array, returning a new array.
Uses the Fisher-Yates algorithm to reorder the elements of the array.
const shuffle = ([...arr]) => {
let m = arr.length;
while (m) {
const i = Math.floor(Math.random() * m--);
[arr[m], arr[i]] = [arr[i], arr[m]];
}
return arr;
};
Examples
const foo = [1, 2, 3];
shuffle(foo); // [2, 3, 1], foo = [1, 2, 3]
similarity
Returns an array of elements that appear in both arrays.
Use Array.prototype.filter() to remove values that are not part of values, determined using Array.prototype.includes().
const similarity = (arr, values) => arr.filter(v => values.includes(v));
Examples
similarity([1, 2, 3], [1, 2, 4]); // [1, 2]
sortedIndex
Returns the lowest index at which value should be inserted into array in order to maintain its sort order.
Check if the array is sorted in descending order (loosely). Use Array.prototype.findIndex() to find the appropriate index where the element should be inserted.
const sortedIndex = (arr, n) => {
const isDescending = arr[0] > arr[arr.length - 1];
const index = arr.findIndex(el => (isDescending ? n >= el : n <= el));
return index === -1 ? arr.length : index;
};
Examples
sortedIndex([5, 3, 2, 1], 4); // 1
sortedIndex([30, 50], 40); // 1
sortedIndexBy
Returns the lowest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.
Check if the array is sorted in descending order (loosely). Use Array.prototype.findIndex() to find the appropriate index where the element should be inserted, based on the iterator function fn.
const sortedIndexBy = (arr, n, fn) => {
const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
const val = fn(n);
const index = arr.findIndex(el => (isDescending ? val >= fn(el) : val <= fn(el)));
return index === -1 ? arr.length : index;
};
Examples
sortedIndexBy([{ x: 4 }, { x: 5 }], { x: 4 }, o => o.x); // 0
sortedLastIndex
Returns the highest index at which value should be inserted into array in order to maintain its sort order.
Check if the array is sorted in descending order (loosely). Use Array.prototype.reverse() and Array.prototype.findIndex() to find the appropriate last index where the element should be inserted.
const sortedLastIndex = (arr, n) => {
const isDescending = arr[0] > arr[arr.length - 1];
const index = arr.reverse().findIndex(el => (isDescending ? n <= el : n >= el));
return index === -1 ? 0 : arr.length - index;
};
Examples
sortedLastIndex([10, 20, 30, 30, 40], 30); // 4
sor
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