Subtraction assignment (-=)
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 subtraction assignment (-=
) operator performs subtraction on the two operands and assigns the result to the left operand.
Try it
let a = 2;
console.log((a -= 3));
// Expected output: -1
console.log((a -= "Hello"));
// Expected output: NaN
Syntax
js
x -= y
Description
x -= y
is equivalent to x = x - y
, except that the expression x
is only evaluated once.
Examples
Subtraction assignment using numbers
js
let bar = 5;
bar -= 2; // 3
Other non-BigInt values are coerced to numbers:
js
bar -= "foo"; // NaN
Subtraction assignment using BigInts
js
let foo = 3n;
foo -= 2n; // 1n
foo -= 1; // TypeError: Cannot mix BigInt and other types, use explicit conversions
Specifications
Specification |
---|
ECMAScript® 2025 Language Specification # sec-assignment-operators |
Browser compatibility
Report problems with this compatibility data on GitHubdesktop | mobile | server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Subtraction assignment ( x -= y ) |
Legend
Tip: you can click/tap on a cell for more information.
- Full support
- Full support
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.