BigInt.asUintN()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2020.
The BigInt.asUintN()
static method truncates a BigInt
value to the given number of least significant bits and returns that value as an unsigned integer.
Try it
const U64_CEIL = 2n ** 64n;
console.log(BigInt.asUintN(64, U64_CEIL - 1n));
// 18446744073709551615n (2n ** 64n - 1n, the maximum non-wrapping value)
console.log(BigInt.asUintN(64, U64_CEIL));
// 0n (wraps to zero)
console.log(BigInt.asUintN(64, U64_CEIL + 1n));
// 1n
console.log(BigInt.asUintN(64, U64_CEIL * 2n));
// 0n (wraps on multiples)
console.log(BigInt.asUintN(64, U64_CEIL * -42n));
// 0n (also wraps on negative multiples)
Syntax
BigInt.asUintN(bits, bigint)
Parameters
Return value
The value of bigint
modulo 2^bits
, as an unsigned integer.
Exceptions
RangeError
-
Thrown if
bits
is negative or greater than 253 - 1.
Description
The BigInt.asUintN
method truncates a BigInt
value to the given number of bits, and interprets the result as an unsigned integer. Unsigned integers have no sign bits and are always non-negative. For example, for BigInt.asUintN(4, 25n)
, the value 25n
is truncated to 9n
:
25n = 00011001 (base 2) ^==== Use only the four remaining bits ===> 1001 (base 2) = 9n
Note: BigInt
values are always encoded as two's complement in binary.
Unlike similar language APIs such as Number.prototype.toExponential()
, asUintN
is a static property of BigInt
, so you always use it as BigInt.asUintN()
, rather than as a method of a BigInt value. Exposing asUintN()
as a "standard library function" allows interop with asm.js.
Examples
Staying in 64-bit ranges
The BigInt.asUintN()
method can be useful to stay in the range of 64-bit arithmetic.
const max = 2n ** 64n - 1n;
BigInt.asUintN(64, max); // 18446744073709551615n
BigInt.asUintN(64, max + 1n); // 0n
// zero because of overflow: the lowest 64 bits are all zeros
Specifications
Specification |
---|
ECMAScript® 2025 Language Specification # sec-bigint.asuintn |
Browser compatibility
Report problems with this compatibility data on GitHubdesktop | mobile | server | ||||||||||||
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asUintN |
Legend
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