BigInt.asIntN()
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.asIntN()
static method truncates a BigInt
value to the given number of least significant bits and returns that value as a signed integer.
Try it
Syntax
BigInt.asIntN(bits, bigint)
Parameters
Return value
The value of bigint
modulo 2^bits
, as a signed integer.
Exceptions
RangeError
-
Thrown if
bits
is negative or greater than 253 - 1.
Description
The BigInt.asIntN
method truncates a BigInt
value to the given number of bits, and interprets the result as a signed integer. For example, for BigInt.asIntN(3, 25n)
, the value 25n
is truncated to 1n
:
25n = 00011001 (base 2) ^=== Use only the three remaining bits ===> 001 (base 2) = 1n
If the leading bit of the remaining number is 1
, the result is negative. For example, BigInt.asIntN(4, 25n)
yields -7n
, because 1001
is the encoding of -7
under two's complement:
25n = 00011001 (base 2) ^==== Use only the four remaining bits ===> 1001 (base 2) = -7n
Note: BigInt
values are always encoded as two's complement in binary.
Unlike similar language APIs such as Number.prototype.toExponential()
, asIntN
is a static property of BigInt
, so you always use it as BigInt.asIntN()
, rather than as a method of a BigInt value. Exposing asIntN()
as a "standard library function" allows interop with asm.js.
Examples
Staying in 64-bit ranges
The BigInt.asIntN()
method can be useful to stay in the range of 64-bit arithmetic.
const max = 2n ** (64n - 1n) - 1n;
BigInt.asIntN(64, max); // 9223372036854775807n
BigInt.asIntN(64, max + 1n); // -9223372036854775808n
// negative because the 64th bit of 2^63 is 1
Specifications
Specification |
---|
ECMAScript Language Specification # sec-bigint.asintn |
Browser compatibility
BCD tables only load in the browser