The static Atomics.or() method computes a bitwise OR with a given value at a given position in the array, and returns the old value at that position. This atomic operation guarantees that no other write happens until the modified value is written back.

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Atomics.or(typedArray, index, value)



An integer typed array. One of Int8Array, Uint8Array, Int16Array, Uint16Array, Int32Array, Uint32Array, BigInt64Array, or BigUint64Array.


The position in the typedArray to compute the bitwise OR.


The number to compute the bitwise OR with.

Return value

The old value at the given position (typedArray[index]).


  • Throws a TypeError, if typedArray is not one of the allowed integer types.
  • Throws a RangeError, if index is out of bounds in the typedArray.


The bitwise OR operation yields 1, if either a or b are 1. The truth table for the OR operation is:

a b a | b
0 0 0
0 1 1
1 0 1
1 1 1

For example, a bitwise OR of 5 | 1 results in 0101 which is 5 in decimal.

5  0101
1  0001
5  0101


Using or

const sab = new SharedArrayBuffer(1024);
const ta = new Uint8Array(sab);
ta[0] = 2;

Atomics.or(ta, 0, 1); // returns 2, the old value
Atomics.load(ta, 0);  // 3


ECMAScript Language Specification
# sec-atomics.or

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See also