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---
title: Left shift assignment (<<=)
slug: Web/JavaScript/Reference/Operators/Left_shift_assignment
page-type: javascript-operator
browser-compat: javascript.operators.left_shift_assignment
---
{{jsSidebar("Operators")}}
The **left shift assignment (`<<=`)** operator performs [left shift](/en-US/docs/Web/JavaScript/Reference/Operators/Left_shift) on the two operands and assigns the result to the left operand.
{{EmbedInteractiveExample("pages/js/expressions-left-shift-assignment.html", "shorter")}}
## Syntax
```js-nolint
x <<= y
```
## Description
`x <<= y` is equivalent to `x = x << y`, except that the expression `x` is only evaluated once.
## Examples
### Using left shift assignment
```js
let a = 5;
// 00000000000000000000000000000101
a <<= 2; // 20
// 00000000000000000000000000010100
let b = 5n;
b <<= 2n; // 20n
```
## Specifications
{{Specifications}}
## Browser compatibility
{{Compat}}
## See also
- [Assignment operators in the JS guide](/en-US/docs/Web/JavaScript/Guide/Expressions_and_operators#assignment_operators)
- [Left shift (`<<`)](/en-US/docs/Web/JavaScript/Reference/Operators/Left_shift)