files/zh-cn/web/javascript/reference/operators/left_shift_assignment/index.md


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---
title: 左移赋值 (<<=)
slug: Web/JavaScript/Reference/Operators/Left_shift_assignment
tags:
  - Assignment operator
  - JavaScript
  - Language feature
  - Operator
  - Reference
browser-compat: javascript.operators.left_shift_assignment
---
{{jsSidebar("Operators")}}

左移赋值运算符 (`<<=`) 将变量向左移动指定数量的位，并将结果赋值给变量。

{{EmbedInteractiveExample("pages/js/expressions-left-shift-assignment.html")}}

## 语法

```js
x <<= y // x = x << y
```

## 例子

### 使用左移赋值

```js
let a = 5;
// 00000000000000000000000000000101

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

## 规范

{{Specifications}}

## 浏览器兼容性

{{Compat("javascript.operators.left_shift_assignment")}}

## 参考

- [JS 指南中的赋值运算符](/zh-CN/docs/Web/JavaScript/Guide/Expressions_and_Operators#assignment)
- [左移运算符](/zh-CN/docs/Web/JavaScript/Reference/Operators/Left_shift)