src/third_party/mozjs-45/js/src/jit-test/tests/proxy/testDirectProxyKeys9.js

// Cull non-existent names returned by the trap.
var nullProtoAB = Object.create(null, {
    a: {
        enumerable: true,
        configurable: true
    },
    b: {
        enumerable: false,
        configurable: true
    }
});
var protoABWithCD = Object.create(nullProtoAB, {
    c: {
        enumerable: true,
        configurable: true
    },
    d: {
        enumerable: false,
        configurable: true
    }
});

var returnedNames;
var handler = { ownKeys: () => returnedNames };

for (let p of [new Proxy(protoABWithCD, handler), Proxy.revocable(protoABWithCD, handler).proxy]) {
    returnedNames = [ 'e' ];
    var names = Object.keys(p);
    assertEq(names.length, 0);

    returnedNames = [ 'c' ];
    names = Object.keys(p);
    assertEq(names.length, 1);
    assertEq(names[0], 'c');
}