JezK
Edit File: override-read-only-property.js
// Copyright 2009 the V8 project authors. All rights reserved. // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above // copyright notice, this list of conditions and the following // disclaimer in the documentation and/or other materials provided // with the distribution. // * Neither the name of Google Inc. nor the names of its // contributors may be used to endorse or promote products derived // from this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. // According to ECMA-262, sections 8.6.2.2 and 8.6.2.3 you're not // allowed to override read-only properties, not even if the read-only // property is in the prototype chain. // // However, for compatibility with WebKit/JSC, we allow the overriding // of read-only properties in prototype chains. function F() {}; F.prototype = Number; var original_number_max = Number.MAX_VALUE; // Assignment to a property which does not exist on the object itself, // but is read-only in a prototype takes effect. var f = new F(); assertEquals(original_number_max, f.MAX_VALUE); f.MAX_VALUE = 42; assertEquals(42, f.MAX_VALUE); // Assignment to a property which does not exist on the object itself, // but is read-only in a prototype takes effect. f = new F(); with (f) { MAX_VALUE = 42; } assertEquals(42, f.MAX_VALUE); // Assignment to read-only property on the object itself is ignored. Number.MAX_VALUE = 42; assertEquals(original_number_max, Number.MAX_VALUE); // G should be read-only on the global object and the assignment is // ignored. (function G() { eval("G = 42;"); assertTrue(typeof G === 'function'); })();