Decrement (--)

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 decrement (--) operator decrements (subtracts one from) its operand and returns the value before or after the decrement, depending on where the operator is placed.

Try it

let x = 3;
const y = x--;

console.log(`x:${x}, y:${y}`);
// Expected output: "x:2, y:3"

let a = 3;
const b = --a;

console.log(`a:${a}, b:${b}`);
// Expected output: "a:2, b:2"

Syntax

js
x--
--x

Description

The -- operator is overloaded for two types of operands: number and BigInt. It first coerces the operand to a numeric value and tests the type of it. It performs BigInt decrement if the operand becomes a BigInt; otherwise, it performs number decrement.

If used postfix, with operator after operand (for example, x--), the decrement operator decrements and returns the value before decrementing.

If used prefix, with operator before operand (for example, --x), the decrement operator decrements and returns the value after decrementing.

The decrement operator can only be applied on operands that are references (variables and object properties; i.e. valid assignment targets). --x itself evaluates to a value, not a reference, so you cannot chain multiple decrement operators together.

js
--(--x); // SyntaxError: Invalid left-hand side expression in prefix operation

Examples

Postfix decrement

js
let x = 3;
const y = x--;
// x is 2; y is 3

let x2 = 3n;
const y2 = x2--;
// x2 is 2n; y2 is 3n

Prefix decrement

js
let x = 3;
const y = --x;
// x is 2; y = 2

let x2 = 3n;
const y2 = --x2;
// x2 is 2n; y2 is 2n

Specifications

Specification
ECMAScript® 2025 Language Specification
# sec-postfix-decrement-operator

Browser compatibility

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
Decrement (--)

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support

See also