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• 描述
• 构造函数
• 静态特性
• 静态方法
• 实例方法
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

Number 是 原语包裹器对象 用于表示和操纵数字，像 37 or -9.25 .

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

JavaScript Number type is a 双精度 64 位二进制格式 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 1.8×10 ³⁰⁸ . 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 .

描述

当用作函数时， Number(value) converts a string or other value to the Number type. If the value can't be converted, it returns NaN .

文字句法

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

函数句法

Number('123')  // returns the number 123
Number('123') === 123  // true
Number("unicorn")  // NaN
Number(undefined)  // NaN
				

构造函数

Number()

创建新的 Number 值。

静态特性

Number.EPSILON

The smallest interval between two representable numbers.

Number.MAX_SAFE_INTEGER

The maximum safe integer in JavaScript ( 2 53 - 1 ).

Number.MAX_VALUE

The largest positive representable number.

Number.MIN_SAFE_INTEGER

The minimum safe integer in JavaScript ( -(2 53 - 1) ).

Number.MIN_VALUE

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

Number.NaN

Special " N ot a N umber" 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 对象。

静态方法

Number.isNaN()

确定传递的值是否为 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 -(2 53 - 1) and 2 53 - 1 ).

Number.parseFloat( string )

This is the same as the global parseFloat() 函数。

Number.parseInt( string , [ radix ])

This is the same as the global parseInt() 函数。

实例方法

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() 方法。

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() 方法。

Number.prototype.valueOf()

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

范例

使用 Number 对象把值赋值给数值变量在该规范中的 load 定义。

以下范例使用 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
					

数字的整数范围

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 类型。

A possible workaround is to use String 代替。

Larger numbers can be represented using the BigInt 类型。

使用数字转换日期对象

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 .

把数值字符串和 null 转换为数字

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
					

规范

规范
ECMAScript (ECMA-262) 在该规范中的 Number 定义。

浏览器兼容性

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.

更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
Number	Chrome 1	Edge 12	Firefox 1	IE 3	Opera 3	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
EPSILON	Chrome 34	Edge 12	Firefox 25	IE No	Opera 21	Safari 9	WebView Android ≤37	Chrome Android 34	Firefox Android 25	Opera Android 21	Safari iOS 9	Samsung Internet Android 2.0	nodejs 0.12
MAX_SAFE_INTEGER	Chrome 34	Edge 12	Firefox 31	IE No	Opera 21	Safari 9	WebView Android ≤37	Chrome Android 34	Firefox Android 31	Opera Android 21	Safari iOS 9	Samsung Internet Android 2.0	nodejs 0.12
MAX_VALUE	Chrome 1	Edge 12	Firefox 1	IE 4	Opera 3	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
MIN_SAFE_INTEGER	Chrome 34	Edge 12	Firefox 31	IE No	Opera 21	Safari 9	WebView Android ≤37	Chrome Android 34	Firefox Android 31	Opera Android 21	Safari iOS 9	Samsung Internet Android 2.0	nodejs 0.12
MIN_VALUE	Chrome 1	Edge 12	Firefox 1	IE 4	Opera 3	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
NaN	Chrome 1	Edge 12	Firefox 1	IE 4	Opera 3	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
NEGATIVE_INFINITY	Chrome 1	Edge 12	Firefox 1	IE 4	Opera 3	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
Number() 构造函数	Chrome 1	Edge 12	Firefox 1	IE 3	Opera 3	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
POSITIVE_INFINITY	Chrome 1	Edge 12	Firefox 1	IE 4	Opera 3	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
isFinite	Chrome 19	Edge 12	Firefox 16	IE No	Opera 15	Safari 9	WebView Android ≤37	Chrome Android 25	Firefox Android 16	Opera Android 14	Safari iOS 9	Samsung Internet Android 1.5	nodejs 0.10
isInteger	Chrome 34	Edge 12	Firefox 16	IE No	Opera 21	Safari 9	WebView Android ≤37	Chrome Android 34	Firefox Android 16	Opera Android 21	Safari iOS 9	Samsung Internet Android 2.0	nodejs 0.12
isNaN	Chrome 25	Edge 12	Firefox 15	IE No	Opera 15	Safari 9	WebView Android ≤37	Chrome Android 25	Firefox Android 15	Opera Android 14	Safari iOS 9	Samsung Internet Android 1.5	nodejs 0.10
isSafeInteger	Chrome 34	Edge 12	Firefox 32	IE No	Opera 21	Safari 10	WebView Android ≤37	Chrome Android 34	Firefox Android 32	Opera Android 21	Safari iOS 10	Samsung Internet Android 2.0	nodejs 0.12
parseFloat	Chrome 34	Edge 12	Firefox 25	IE No	Opera 21	Safari 9	WebView Android ≤37	Chrome Android 34	Firefox Android 25	Opera Android 21	Safari iOS 9	Samsung Internet Android 2.0	nodejs 0.12
parseInt	Chrome 34	Edge 12	Firefox 25	IE No	Opera 21	Safari 9	WebView Android ≤37	Chrome Android 34	Firefox Android 25	Opera Android 21	Safari iOS 9	Samsung Internet Android 2.0	nodejs 0.12
toExponential	Chrome 1	Edge 12	Firefox 1	IE 5.5	Opera 7	Safari 2	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
toFixed	Chrome 1	Edge 12	Firefox 1	IE 5.5	Opera 7	Safari 2	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
toLocaleString	Chrome 1	Edge 12 12 Before Edge 18, numbers are rounded to 15 decimal digits. For example, (1000000000000005).toLocaleString('en-US') 返回 "1,000,000,000,000,010" .	Firefox 1	IE 5 5 In Internet Explorer 11, numbers are rounded to 15 decimal digits. For example, (1000000000000005).toLocaleString('en-US') 返回 "1,000,000,000,000,010" .	Opera 4	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
toPrecision	Chrome 1	Edge 12	Firefox 1	IE 5.5	Opera 7	Safari 2	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
toSource 非标	Chrome No	Edge No	Firefox 1 — 74 不支持 1 — 74 Starting in Firefox 74, toSource() is no longer available for use by web content. It is still allowed for internal and privileged code.	IE No	Opera No	Safari No	WebView Android No	Chrome Android No	Firefox Android 4	Opera Android No	Safari iOS No	Samsung Internet Android No	nodejs No
toString	Chrome 1	Edge 12	Firefox 1	IE 3	Opera 4	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100
valueOf	Chrome 1	Edge 12	Firefox 1	IE 4	Opera 4	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs 0.1.100

图例

完整支持

完整支持

不支持

不支持

非标。预期跨浏览器支持较差。

非标。预期跨浏览器支持较差。

见实现注意事项。

另请参阅

• NaN
• 算术运算符
• Math 全局对象
• 具有任意精度的整数： BigInt

元数据

• 最后修改： Jul 15, 2020

相关话题

1. 标准内置对象
2. Number
3. 特性
   1. Number.EPSILON
   2. Number.MAX_SAFE_INTEGER
   3. Number.MAX_VALUE
   4. Number.MIN_SAFE_INTEGER
   5. Number.MIN_VALUE
   6. Number.NEGATIVE_INFINITY
   7. Number.NaN
   8. Number.POSITIVE_INFINITY
4. 方法
   1. Number.isFinite()
   2. Number.isInteger()
   3. Number.isNaN()
   4. Number.isSafeInteger()
   5. Number.parseFloat()
   6. Number.parseInt()
   7. Number.prototype.toExponential()
   8. Number.prototype.toFixed()
   9. Number.prototype.toLocaleString()
   10. Number.prototype.toPrecision()
   11. Number.prototype.toSource()
   12. Number.prototype.toString()
   13. Number.prototype.valueOf()
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
9. Object
10. 特性
    1. Object.prototype.__proto__
    2. Object.prototype.constructor
11. 方法
    1. Object.prototype.__defineGetter__()
    2. Object.prototype.__defineSetter__()
    3. Object.prototype.__lookupGetter__()
    4. Object.prototype.__lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. Object.prototype.isPrototypeOf()
    7. Object.prototype.propertyIsEnumerable()
    8. Object.prototype.toLocaleString()
    9. Object.prototype.toSource()
    10. Object.prototype.toString()
    11. Object.prototype.valueOf()
    12. Object.setPrototypeOf()