Subtraction assignment (-=)

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The subtraction assignment (-=) operator performs subtraction on the two operands and assigns the result to the left operand.

{{InteractiveExample("JavaScript Demo: Subtraction assignment (-=) operator")}}

```js interactive-example let a = 2;

console.log((a -= 3)); // Expected output: -1

console.log((a -= "Hello")); // Expected output: NaN

## Syntax

```js-nolint
x -= y

Description#

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