Remainder assignment (%=)

The remainder assignment (%=) operator performs remainder 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; // 1
bar %= "foo"; // NaN
bar %= 0; // NaN

let foo = 3n;
foo %= 2n; // 1n

Specification
ECMAScript Language Specification # sec-assignment-operators

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