Number

Baseline

20157

Number 37 -9.25

Number Number()

255 3.14159

255; // 
255.0; // 
255 === 255.0; // true
255 === 0xff; // true 16 
255 === 0b11111111; // true 2 
255 === 0.255e3; // true 10

JavaScript 37 JavaScript (BigInt) 37

Number(value) NaN

Number("123"); //  123 
Number("123") === 123; // true

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

JavaScript (Number) IEEE 754 64 Java C# double IEEE 754 3 64

1 sign,
11 exponent, -1022 1023
52 mantissa, 0 1

significand 2

Number=(1)sign(1+mantissa)2exponent\text{Number} = ({-1})^{\text{sign}} \cdot (1 + \text{mantissa}) \cdot 2^{\text{exponent}}

52 2 1. 2-52Number.EPSILON 10 15 17

21023 (2 - 2-52)2 1023 0.1111... Number.MAX_VALUE Infinity

53 1 -253 + 1 253 - 1 Number.MIN_SAFE_INTEGER Number.MAX_SAFE_INTEGER

ECMAScript

Number

undefined NaN
null 0
true 1 false 0
NaN
- /
- 0 8
- + -
- Infinity -Infinity
- 0
TypeError
TypeError
[Symbol.toPrimitive]() "number" valueOf()toString()

JavaScript 2

: +x x
Number() : Number(x) x TypeError

Number.parseFloat() Number.parseInt() Number() parseInt() parseFloat() 0x

(Infinity) NaN -0 0 -0 Infinity

undefined null 0 undefined NaN 0

JavaScript 2 TypedArray 32 2

new Int32Array([1.1, 1.9, -1.1, -1.9]); // Int32Array(4) [ 1, 1, -1, -1 ]

new Int8Array([257, -257]); // Int8Array(2) [ 1, -1 ]
// 257 = 0001 0000 0001
//     =      0000 0001 (mod 2^8)
//     = 1
// -257 = 1110 1111 1111
//      =      1111 1111 (mod 2^8)
//      = -1 (as signed integer)

new Uint8Array([257, -257]); // Uint8Array(2) [ 1, 255 ]
// -257 = 1110 1111 1111
//      =      1111 1111 (mod 2^8)
//      = 255 (as unsigned integer)

Number(): Number

Number.EPSILON: 2
Number.MAX_SAFE_INTEGER: JavaScript (253 - 1)
Number.MAX_VALUE
Number.MIN_SAFE_INTEGER: JavaScript (-(253 - 1))
Number.MIN_VALUE: 0 0
Number.NaN: "Not a Number"
Number.NEGATIVE_INFINITY
Number.POSITIVE_INFINITY

Number.isFinite()
Number.isInteger()
Number.isNaN(): NaN
Number.isSafeInteger(): -(253 - 1) 253 - 1
Number.parseFloat(): parseFloat()
Number.parseInt(): parseInt()

Number.prototype Number

Number.prototype.constructor: Number Number

Number.prototype.toExponential()
Number.prototype.toFixed()
Number.prototype.toLocaleString(): Object.prototype.toLocaleString()
Number.prototype.toPrecision()
Number.prototype.toString(): Object.prototype.toString()
Number.prototype.valueOf(): Object.prototype.valueOf()

Number

Number

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

Number

Number

const biggestInt = Number.MAX_SAFE_INTEGER; // (2**53 - 1) => 9007199254740991
const smallestInt = Number.MIN_SAFE_INTEGER; // -(2**53 - 1) => -9007199254740991

JSON JSON Number

String

BigInt

Number Date

Number Date

const d = new Date("December 17, 1995 03:24:00");
console.log(Number(d));

819199440000

null

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


ECMAScript 2027 LanguageSpecification # sec-number-objects

MDN

MDN 2026627

GitHub