Multiplication assignment (*=)

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

Try it

x *= y

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

let bar = 5;
bar *= 2; // 10

Other non-BigInt values are coerced to numbers:

let bar = 5;
bar *= "foo"; // NaN

let foo = 3n;
foo *= 2n; // 6n
foo *= 1; // TypeError: Cannot mix BigInt and other types, use explicit conversions

Specification
ECMAScript Language Specification # sec-assignment-operators

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