src/third_party/mozjs-45/js/src/jit-test/tests/basic/bug1106982-2.js

var x = "wrong";
var t = {x: "x"};
var hits = 0;
var p = new Proxy(t, {
    has(t, id) {
        var found = id in t;
        if (++hits == 2)
            delete t[id];
        return found;
    },
    get(t, id) { return t[id]; }
});
evaluate(`function testFunc() {
    x += " x";
}`);

var cloneFunc = clone(testFunc, p);
cloneFunc();
assertEq(hits, 2);
assertEq(t.x, "undefined x");