TheBigInt.asUintN() static method truncates aBigInt 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));// 1nconsole.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

bits

The amount of bits available for the returned BigInt. Should be an integer between 0 and 2⁵³ - 1, inclusive.

bigint

The BigInt value to truncate to fit into the supplied bits.

Return value

The value ofbigint modulo2 ** bits, as an unsigned integer.

Exceptions

RangeError

Thrown ifbits is negative or greater than 2⁵³ - 1.

Description

TheBigInt.asUintN method truncates aBigInt 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, forBigInt.asUintN(4, 25n), the value25n is truncated to9n:

25n = 00011001 (base 2)         ^==== Use only the four remaining bits===>      1001 (base 2) = 9n

Unlike similar language APIs such asNumber.prototype.toExponential(),asUintN is a static property ofBigInt, so you always use it asBigInt.asUintN(), rather than as a method of a BigInt value. ExposingasUintN() as a "standard library function" allowsinterop with asm.js.

Examples

Staying in 64-bit ranges

TheBigInt.asUintN() method can be useful to stay in the range of 64-bit arithmetic.

const max = 2n ** 64n - 1n;BigInt.asUintN(64, max); // 18446744073709551615nBigInt.asUintN(64, max + 1n); // 0n// zero because of overflow: the lowest 64 bits are all zeros

Specifications

Browser compatibility

See also

• BigInt
• BigInt.asIntN()