BigInt - JavaScript 编辑

BigInt is a built-in object that provides a way to represent whole numbers larger than 2⁵³ - 1, which is the largest number JavaScript can reliably represent with the Number primitive and represented by the Number.MAX_SAFE_INTEGER constant. BigInt can be used for arbitrarily large integers.

Description

A BigInt is created by appending n to the end of an integer literal — 10n — or by calling the function BigInt().

const previouslyMaxSafeInteger = 9007199254740991n

const alsoHuge = BigInt(9007199254740991)
// ↪ 9007199254740991n

const hugeString = BigInt("9007199254740991")
// ↪ 9007199254740991n

const hugeHex = BigInt("0x1fffffffffffff")
// ↪ 9007199254740991n

const hugeOctal = BigInt("0o377777777777777777")
// ↪ 9007199254740991n

const hugeBin = BigInt("0b11111111111111111111111111111111111111111111111111111")
// ↪ 9007199254740991n

BigInt is similar to Number in some ways, but also differs in a few key matters — it cannot be used with methods in the built-in Math object and cannot be mixed with instances of Number in operations; they must be coerced to the same type. Be careful coercing values back and forth, however, as the precision of a BigInt may be lost when it is coerced to a Number.

Type information

When tested against typeof, a BigInt will give "bigint":

typeof 1n === 'bigint'           // true
typeof BigInt('1') === 'bigint'  // true

When wrapped in an Object, a BigInt will be considered as a normal "object" type:

typeof Object(1n) === 'object'  // true

Operators

The following operators may be used with BigInts (or object-wrapped BigInts): +, *, -, **, %.

Bitwise operators are supported as well, except >>> (zero-fill right shift) as all BigInts are signed.

Also unsupported is the unary operator (+), in order to not break asm.js.

const previousMaxSafe = BigInt(Number.MAX_SAFE_INTEGER)
// ↪ 9007199254740991n

const maxPlusOne = previousMaxSafe + 1n
// ↪ 9007199254740992n

const theFuture = previousMaxSafe + 2n
// ↪ 9007199254740993n, this works now!

const multi = previousMaxSafe * 2n
// ↪ 18014398509481982n

const subtr = multi – 10n
// ↪ 18014398509481972n

const mod = multi % 10n
// ↪ 2n

const bigN = 2n ** 54n
// ↪ 18014398509481984n

bigN * -1n
// ↪ –18014398509481984n

The / operator also works as expected with whole numbers.

However, since these are BigInts and not BigDecimals, this operation will round towards 0 (which is to say, it will not return any fractional digits).

An operation with a fractional result will be truncated when used with a BigInt.

const expected = 4n / 2n
// ↪ 2n

const rounded = 5n / 2n
// ↪ 2n, not 2.5n

Comparisons

A BigInt is not strictly equal to a Number, but it is loosely so:

0n === 0
// ↪ false

0n == 0
// ↪ true

A Number and a BigInt may be compared as usual:

1n < 2
// ↪ true

2n > 1
// ↪ true

2 > 2
// ↪ false

2n > 2
// ↪ false

2n >= 2
// ↪ true

They may be mixed in arrays and sorted:

const mixed = [4n, 6, -12n, 10, 4, 0, 0n]
// ↪  [4n, 6, -12n, 10, 4, 0, 0n]

mixed.sort() // default sorting behavior
// ↪  [ -12n, 0, 0n, 10, 4n, 4, 6 ]

mixed.sort((a, b) => a - b)
// won't work since subtraction will not work with mixed types
// TypeError: can't convert BigInt to number

// sort with an appropriate numeric comparator
mixed.sort((a, b) => (a < b) ? -1 : ((a > b) ? 1 : 0))
// ↪  [ -12n, 0, 0n, 4n, 4, 6, 10 ]

Note that comparisons with Object-wrapped BigInts act as with other objects, only indicating equality when the same object instance is compared:

0n === Object(0n)          // false
Object(0n) === Object(0n)  // false

const o = Object(0n)
o === o                    // true

Conditionals

A BigInt behaves like a Number in cases where:

• it is converted to a Boolean: via the Boolean function;
• when used with logical operators ||, &&, and !; or
• within a conditional test like an if statement.

if (0n) {
  console.log('Hello from the if!')
} else {
  console.log('Hello from the else!')
}

// ↪ "Hello from the else!"

0n || 12n
// ↪ 12n

0n && 12n
// ↪ 0n

Boolean(0n)
// ↪ false

Boolean(12n)
// ↪ true

!12n
// ↪ false

!0n
// ↪ true

Constructor

BigInt()

Creates a new bigint value.

Static methods

BigInt.asIntN()

Wraps a BigInt value to a signed integer between -2width-1 and 2width-1 - 1.

BigInt.asUintN()

Wraps a BigInt value to an unsigned integer between 0 and 2width - 1.

Instance methods

BigInt.prototype.toLocaleString()

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

BigInt.prototype.toString()

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

BigInt.prototype.valueOf()

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

Usage recommendations

Coercion

Because coercing between Number and BigInt can lead to loss of precision, it is recommended to only use BigInt when values greater than 2⁵³ are reasonably expected and not to coerce between the two types.

Cryptography

The operations supported on BigInts are not constant time. BigInt is therefore unsuitable for use in cryptography.

Use within JSON

Using JSON.stringify() with any BigInt value will raise a TypeError as BigInt values aren't serialized in JSON by default. However, you can implement your own toJSON method if needed:

BigInt.prototype.toJSON = function() { return this.toString()  }

Instead of throwing, JSON.stringify now produces a string like this:

JSON.stringify(BigInt(1))
// '"1"'

Examples

Calculating Primes

// Returns true if passed BigInt is a prime number
function isPrime(p) {
  for (let i = 2n; i * i <= p; i++) {
    if (p % i === 0n) return false;
  }
  return true
}

// Takes a BigInt as an argument, returns nth prime number as BigInt
function nthPrime(nth) {
  let maybePrime = 2n
  let prime = 0n

  while (nth >= 0n) {
    if (isPrime(maybePrime)) {
      nth--
      prime = maybePrime
    }
    maybePrime++
  }

  return prime
}

nthPrime(20n)
// ↪ 73n

Specifications

Specification
ECMAScript (ECMA-262) The definition of 'BigInt objects' in that specification.

Browser compatibility

BCD tables only load in the browser

The compatibility table on 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.

Implementation Progress

The following table provides a daily implementation status for this feature, because this feature has not yet reached cross-browser stability. The data is generated by running the relevant feature tests in Test262, the standard test suite of JavaScript, in the nightly build, or latest release of each browser's JavaScript engine.

See also

• Number
• Number.MAX_SAFE_INTEGER