Number - JavaScript 编辑

The Number constructor contains constants and methods for working with numbers. Values of other types can be converted to numbers using the Number() function.

The JavaScript Number type is a double-precision 64-bit binary format IEEE 754 value, like double in Java or C#. This means it can represent fractional values, but there are some limits to what it can store. A Number only keeps about 17 decimal places of precision; arithmetic is subject to rounding. The largest value a Number can hold is about 1.8×10³⁰⁸. Numbers beyond that are replaced with the special Number constant Infinity.

A number literal like 37 in JavaScript code is a floating-point value, not an integer. There is no separate integer type in common everyday use. (JavaScript now has a BigInt type, but it was not designed to replace Number for everyday uses. 37 is still a Number, not a BigInt.)

Number may also be expressed in literal forms like 0b101, 0o13, 0x0A. Learn more on numeric lexical grammar here.

Description

When used as a function, Number(value) converts a string or other value to the Number type. If the value can't be converted, it returns NaN.

Literal syntax

123    // one-hundred twenty-three
123.0  // same
123 === 123.0  // true

Function syntax

Number('123')  // returns the number 123
Number('123') === 123  // true

Number("unicorn")  // NaN
Number(undefined)  // NaN

Constructor

Number()

Creates a new Number value.

Static properties

Number.EPSILON

The smallest interval between two representable numbers.

Number.MAX_SAFE_INTEGER

The maximum safe integer in JavaScript (253 - 1).

Number.MAX_VALUE

The largest positive representable number.

Number.MIN_SAFE_INTEGER

The minimum safe integer in JavaScript (-(253 - 1)).

Number.MIN_VALUE

The smallest positive representable number—that is, the positive number closest to zero (without actually being zero).

Number.NaN

Special "Not a Number" value.

Number.NEGATIVE_INFINITY

Special value representing negative infinity. Returned on overflow.

Number.POSITIVE_INFINITY

Special value representing infinity. Returned on overflow.

Number.prototype

Allows the addition of properties to the Number object.

Static methods

Number.isNaN()

Determine whether the passed value is NaN.

Number.isFinite()

Determine whether the passed value is a finite number.

Number.isInteger()

Determine whether the passed value is an integer.

Number.isSafeInteger()

Determine whether the passed value is a safe integer (number between -(253 - 1) and 253 - 1).

Number.parseFloat(string)

This is the same as the global parseFloat() function.

Number.parseInt(string, [radix])

This is the same as the global parseInt() function.

Instance methods

Number.prototype.toExponential(fractionDigits)

Returns a string representing the number in exponential notation.

Number.prototype.toFixed(digits)

Returns a string representing the number in fixed-point notation.

Number.prototype.toLocaleString([locales [, options]])

Returns a string with a language sensitive representation of this number. Overrides the Object.prototype.toLocaleString() method.

Number.prototype.toPrecision(precision)

Returns a string representing the number to a specified precision in fixed-point or exponential notation.

Number.prototype.toString([radix])

Returns a string representing the specified object in the specified radix ("base"). Overrides the Object.prototype.toString() method.

Number.prototype.valueOf()

Returns the primitive value of the specified object. Overrides the Object.prototype.valueOf() method.

Examples

Using the Number object to assign values to numeric variables

The following example uses the Number object's properties to assign values to several numeric variables:

const biggestNum     = Number.MAX_VALUE
const smallestNum    = Number.MIN_VALUE
const infiniteNum    = Number.POSITIVE_INFINITY
const negInfiniteNum = Number.NEGATIVE_INFINITY
const notANum        = Number.NaN

Integer range for Number

The following example shows the minimum and maximum integer values that can be represented as Number object. (More details on this are described in the ECMAScript standard, chapter 6.1.6 The Number Type.)

const biggestInt  = Number.MAX_SAFE_INTEGER  //  (253 - 1) =>  9007199254740991
const smallestInt = Number.MIN_SAFE_INTEGER  // -(253 - 1) => -9007199254740991

When parsing data that has been serialized to JSON, integer values falling outside of this range can be expected to become corrupted when JSON parser coerces them to Number type.

A possible workaround is to use String instead.

Larger numbers can be represented using the BigInt type.

Using Number to convert a Date object

The following example converts the Date object to a numerical value using Number as a function:

let d = new Date('December 17, 1995 03:24:00')
console.log(Number(d))

This logs 819199440000.

Convert numeric strings and null to numbers

Number('123')     // 123
Number('123') === 123 /// true
Number('12.3')    // 12.3
Number('12.00')   // 12
Number('123e-1')  // 12.3
Number('')        // 0
Number(null)      // 0
Number('0x11')    // 17
Number('0b11')    // 3
Number('0o11')    // 9
Number('foo')     // NaN
Number('100a')    // NaN
Number('-Infinity') //-Infinity

Specifications

Browser compatibility

BCD tables only load in the browser

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• NaN
• Arithmetic operators
• The Math global object
• Integers with arbitrary precision: BigInt