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.

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 Language Specification # sec-assignment-operators

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