test/mjsunit/override-read-only-property.js

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// 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 does not take effect.
var f = new F();
assertEquals(original_number_max, f.MAX_VALUE);
f.MAX_VALUE = 42;
assertEquals(original_number_max, f.MAX_VALUE);

// Assignment to a property which does not exist on the object itself,
// but is read-only in a prototype does not take effect.
f = new F();
with (f) {
  MAX_VALUE = 42;
}
assertEquals(original_number_max, 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');
})();