JSTests/test262/test/built-ins/Proxy/preventExtensions/trap-is-null-target-is-proxy.js

// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.

/*---
esid: sec-proxy-object-internal-methods-and-internal-slots-preventextensions
description: >
  If "preventExtensions" trap is null or undefined, [[PreventExtensions]] call
  is properly forwarded to [[ProxyTarget]] (which is also a Proxy object).
info: |
  [[PreventExtensions]] ( )

  [...]
  4. Let target be O.[[ProxyTarget]].
  5. Let trap be ? GetMethod(handler, "preventExtensions").
  6. If trap is undefined, then
    a. Return ? target.[[PreventExtensions]]().
features: [Proxy]
---*/

var plainObject = {};
var plainObjectTarget = new Proxy(plainObject, {});
var plainObjectProxy = new Proxy(plainObjectTarget, {
  preventExtensions: null,
});

Object.preventExtensions(plainObjectProxy);
assert(!Object.isExtensible(plainObject));