src/third_party/mozjs-45/js/src/jit-test/tests/basic/testObjectToNumber.js

function testObjectToNumber() {
    var o = {valueOf: () => -3};
    var x = 0;
    for (var i = 0; i < 10; i++)
        x -= o;
    return x;
}
assertEq(testObjectToNumber(), 30);