src/third_party/mozjs-45/js/src/jit-test/tests/ion/bug779631.js

var flag = 0;
var a = {};
Object.defineProperty(a, "value", {set: function(x) {}});
a.watch("value", function(){flag++;});

for(var i = 0; i < 100; i++) {
    a.value = i;
    assertEq(flag, i+1);
}