The static Atomics.xor() method computes a bitwise XOR 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.xor(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 XOR.


The number to compute the bitwise XOR 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 XOR operation yields 1, if a and b are different. The truth table for the XOR operation is:

a b a ^ b
0 0 0
0 1 1
1 0 1
1 1 0

For example, a bitwise XOR of 5 ^ 1 results in 0100 which is 4 in decimal.

5  0101
1  0001
4  0100


Using xor

const sab = new SharedArrayBuffer(1024);
const ta = new Uint8Array(sab);
ta[0] = 5;

Atomics.xor(ta, 0, 1); // returns 5, the old value
Atomics.load(ta, 0);  // 4


ECMAScript Language Specification
# sec-atomics.xor

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See also