BigInt.asUintN()

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.

{{InteractiveExample("JavaScript Demo: BigInt.asUintN()", "taller")}}

```js interactive-example 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

```js-nolint
BigInt.asUintN(bits, bigint)

Parameters#

• bits
• : The amount of bits available for the returned BigInt. Should be an integer between 0 and 2<sup>53</sup> - 1, inclusive.
• bigint
• : The BigInt value to truncate to fit into the supplied bits.

Return value#

The value of bigint modulo 2 ** bits, as an unsigned integer.

Exceptions#

• {{jsxref("RangeError")}}
• : Thrown if bits is negative or greater than 2<sup>53</sup> - 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 {{jsxref("Number.prototype.toExponential()")}}, asUintN is a static property of {{jsxref("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#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• {{jsxref("BigInt")}}
• {{jsxref("BigInt.asIntN()")}}