Number.MAX_SAFE_INTEGER - JavaScript 编辑

The Number.MAX_SAFE_INTEGER constant represents the maximum safe integer in JavaScript (253 - 1).

For larger integers, consider using BigInt.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Property attributes of Number.MAX_SAFE_INTEGER
Writable	no
Enumerable	no
Configurable	no

Description

The MAX_SAFE_INTEGER constant has a value of 9007199254740991 (9,007,199,254,740,991 or ~9 quadrillion). The reasoning behind that number is that JavaScript uses double-precision floating-point format numbers as specified in IEEE 754 and can only safely represent integers between -(253 - 1) and 253 - 1.

Safe in this context refers to the ability to represent integers exactly and to correctly compare them. For example, Number.MAX_SAFE_INTEGER + 1 === Number.MAX_SAFE_INTEGER + 2 will evaluate to true, which is mathematically incorrect. See Number.isSafeInteger() for more information.

This field does not exist in old browsers. Using it without checking its existence, such as Math.max(Number.MAX_SAFE_INTEGER, 2), will yield undesired results such as NaN.

Because MAX_SAFE_INTEGER is a static property of Number, you always use it as Number.MAX_SAFE_INTEGER, rather than as a property of a Number object you created.

Polyfill

if (!Number.MAX_SAFE_INTEGER) {
    Number.MAX_SAFE_INTEGER = 9007199254740991; // Math.pow(2, 53) - 1;
}

Examples

Return value of MAX_SAFE_INTEGER

Number.MAX_SAFE_INTEGER; // 9007199254740991

Numbers higher than safe integer

This returns 2 because in floating points, the value is actually the decimal trailing "1" except for in subnormal precision cases such as zero.

Number.MAX_SAFE_INTEGER * Number.EPSILON; // 2

Specifications

Specification
ECMAScript (ECMA-262) The definition of 'Number.MAX_SAFE_INTEGER' in that specification.

Browser compatibility

BCD tables only load in the browser

See also

• Number.MIN_SAFE_INTEGER
• Number.isSafeInteger()
• BigInt