遞增運算子（++）

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since 2015年7月.

遞增運算子（++）遞增（加一）它的運算元並將結果回傳。

嘗試一下

let x = 3;
const y = x++;

console.log(`x:${x}, y:${y}`);
// Expected output: "x:4, y:3"

let a = 3;
const b = ++a;

console.log(`a:${a}, b:${b}`);
// Expected output: "a:4, b:4"

語法

js
x++
++x

詳細說明

若將遞增運算子作為後綴（例如 x++），則會先回傳原本的值，再進行遞增。

若作為前綴（例如 ++x），則會先進行遞增，再將遞增後的結果回傳。

範例

遞增運算子置於後綴

js
let x = 3;
y = x++;

// y = 3
// x = 4

遞增運算子置於前綴

js
let a = 2;
b = ++a;

// a = 3
// b = 3

規範

Specification

ECMAScript® 2027 Language Specification
# sec-postfix-increment-operator

瀏覽器相容性

Enable JavaScript to view this browser compatibility table.

參見

Help improve MDN

Was this page helpful to you?

Yes No

Learn how to contribute

This page was last modified on 2025年7月16日 by MDN contributors.

View this page on GitHub • Report a problem with this content

遞增運算子（++）

In this article

Help improve MDN