src/third_party/mozjs-45/js/src/jit-test/tests/proxy/testDirectProxyPreventExtensions1.js

// Forward to the target if the trap is not defined
var target = {};
var proxy = new Proxy(target, {});
Object.preventExtensions(proxy);
assertEq(Object.isExtensible(target), false);

target = {};
proxy = Proxy.revocable(target, {}).proxy;
Object.preventExtensions(proxy);
assertEq(Object.isExtensible(target), false);