Left shift assignment (<<=)

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The left shift assignment (<<=) operator performs left shift on the two operands and assigns the result to the left operand.

Try it

let a = 5; // 00000000000000000000000000000101

a <<= 2; // 00000000000000000000000000010100

console.log(a);
// Expected output: 20

x <<= y

x <<= y is equivalent to x = x << y, except that the expression x is only evaluated once.

let a = 5;
// 00000000000000000000000000000101

a <<= 2; // 20
// 00000000000000000000000000010100

let b = 5n;
b <<= 2n; // 20n

Specification
ECMAScript® 2026 Language Specification # sec-assignment-operators