The subtraction assignment (-=) operator performs subtraction on the two operands and assigns the result to the left operand.
Syntax
x -= y
Description
x -= y is equivalent to x = x - y, except that the expression x is only evaluated once.
Examples
Using subtraction assignment
let bar = 5;
bar -= 2; // 3
bar -= "foo"; // NaN
let foo = 3n;
foo -= 2n; // 1n