创建新数组时，“new Array(number)”是什么意思？

发布于 2024-10-09 06:59:39 字数 285 浏览 0 评论 0原文

new Array(number) 是什么意思，new Array() 是什么意思？例如：

var weekday=new Array(7);
weekday[0]="Sunday";
weekday[1]="Monday";
weekday[2]="Tuesday";
weekday[3]="Wednesday";
weekday[4]="Thursday";
weekday[5]="Friday";
weekday[6]="Saturday";

原文

What does new Array(number) mean, and what does new Array() mean? For example:

var weekday=new Array(7);
weekday[0]="Sunday";
weekday[1]="Monday";
weekday[2]="Tuesday";
weekday[3]="Wednesday";
weekday[4]="Thursday";
weekday[5]="Friday";
weekday[6]="Saturday";

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你如我软肋 2024-10-16 06:59:39

过去，某些浏览器会预先分配一些空（未定义）数组条目。在我看来，这是毫无意义的，实际上是一个坏习惯，尽管现在这种情况并没有发生。这只是一个奇怪的 API，而奇怪的东西就是 bug 启动器。

你的代码可以更漂亮，例如：

var weekday = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];

我认为 new Array(n) 是一个坏主意的原因是 Array 构造函数的设置有两种模式：

new Array(22);

意味着创建一个 Array 实例22 个空条目，但

new Array(22, 23, 24);

意味着创建一个具有 3 条目的 Array 实例。这是令人困惑和奇怪的，而且真的不应该这样做。

In days of yore, some browsers would pre-allocate some number of empty (undefined) array entries. In my opinion, it's pointless and in fact a bad habit even though that doesn't happen now. It's just a weird API and weird things are bug launchers.

Your code could be much prettier, for example:

var weekday = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];

My reason for thinking that new Array(n) is a bad idea is that the setup of the Array constructor has two modes:

new Array(22);

means to create an Array instance with 22 null entries, but

new Array(22, 23, 24);

means to create an Array instance with 3 entries. It's confusing and weird, and really shouldn't have been done that way.

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迷雾森÷林ヴ 2024-10-16 06:59:39

这
var 工作日 = 新数组( 7 );
正在声明一个包含 7 个项目的数组，如以下几行所示。该数组在每个索引（ number ）处存储值，并且您可以通过变量[#] 访问这些值。

在 javascript 中不需要它，但许多其他语言（例如 Java）需要显式值。

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握住我的手 2024-10-16 06:59:39

Pointy 的回答完美地总结了这一点。只是为了添加另一种选择，您可以这样做（例如，如果您要在循环中执行某些操作而不是对其进行硬编码）：

var weekday = [];
weekday.push("Sunday");
weekday.push("Monday");
weekday.push("Tuesday");
weekday.push("Wednesday");
weekday.push("Thursday");
weekday.push("Friday");
weekday.push("Saturday");

Pointy's answer sums it up perfectly. Just to add another alternative, you could do it like this (if you were to do something in a loop rather than hardcoding it for example):

var weekday = [];
weekday.push("Sunday");
weekday.push("Monday");
weekday.push("Tuesday");
weekday.push("Wednesday");
weekday.push("Thursday");
weekday.push("Friday");
weekday.push("Saturday");

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一杆小烟枪 2024-10-16 06:59:39

var sevenElementsArray = new Array(7);
var emtpryArray1 = new Array();
var emtpryArray2 = [];

数组中的数字构造函数充当容量，但因为数组是动态的，您可以分配：

alert(sevenElementsArray.length); //shows 7
sevenElementsArray[20] = "it's OK";
alert(sevenElementsArray.length); //shows 20
alert(sevenElementsArray[15]); //shows undefined;

同样在 JavaScript 中，您可以通过更新 length 属性来截断和扩大数组。

我建议您阅读 JavaScript：权威指南，第五版，第 7 章：“对象和数组”。您需要了解对象、数组、类数组对象之间的区别。

var sevenElementsArray = new Array(7);
var emtpryArray1 = new Array();
var emtpryArray2 = [];

the number - constructor in an array works as capacity, but cause arrays - are dynamic you may assign:

alert(sevenElementsArray.length); //shows 7
sevenElementsArray[20] = "it's OK";
alert(sevenElementsArray.length); //shows 20
alert(sevenElementsArray[15]); //shows undefined;

also in JavaScript you may truncating and enlarging an array by updating the length property.

I wish to recommend you to read JavaScript: The Definitive Guide, 5th Edition, the chapter 7: "Objects and Arrays". You need to understand difference between object, array, array-like object.

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