左シフト代入 (<<=)

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.

左シフト代入演算子 (<<=) は、指定された数だけビットを左に移動し、結果を変数に代入します。

試してみましょう

let a = 5; // 00000000000000000000000000000101

a <<= 2; // 00000000000000000000000000010100

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

構文

js
x <<= y; // x = x << y

左シフト代入の使用

js
let a = 5;
// 00000000000000000000000000000101

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

仕様書

Specification
ECMAScript® 2025 Language Specification
# sec-assignment-operators

ブラウザーの互換性

Report problems with this compatibility data on GitHub
desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
Left shift assignment (x <<= y)

Legend

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Full support
Full support

関連情報