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

x -= y

x -= y is equivalent to x = x - y, except that the expression x is only evaluated once.

let bar = 5;

bar -= 2; // 3

Other non-BigInt values are coerced to numbers:

bar -= "foo"; // NaN

let foo = 3n;
foo -= 2n; // 1n
foo -= 1; // TypeError: Cannot mix BigInt and other types, use explicit conversions

Specification
ECMAScript® 2027 Language Specification # sec-assignment-operators

	Desktop					Mobile							Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on iOS	Samsung Internet	WebView Android	WebView on iOS	Bun	Deno	Node.js
`subtraction_assignment`	1	12	1	3	1	18	4	10.1	1	1.0	4.4	1	1.0.0	1.0	0.10.0