test/mjsunit/regress/regress-1530.js

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// Test that redefining the 'prototype' property of a function object
// does actually set the internal value and does not screw up any
// shadowing between said property and the internal value.

var f = function() {};

// Verify that normal assignment of 'prototype' property works properly
// and updates the internal value.
var a = { foo: 'bar' };
f.prototype = a;
assertSame(f.prototype, a);
assertSame(f.prototype.foo, 'bar');
assertSame(new f().foo, 'bar');
assertSame(Object.getPrototypeOf(new f()), a);
assertSame(Object.getOwnPropertyDescriptor(f, 'prototype').value, a);
assertTrue(Object.getOwnPropertyDescriptor(f, 'prototype').writable);

// Verify that 'prototype' behaves like a data property when it comes to
// redefining with Object.defineProperty() and the internal value gets
// updated.
var b = { foo: 'baz' };
Object.defineProperty(f, 'prototype', { value: b, writable: true });
assertSame(f.prototype, b);
assertSame(f.prototype.foo, 'baz');
assertSame(new f().foo, 'baz');
assertSame(Object.getPrototypeOf(new f()), b);
assertSame(Object.getOwnPropertyDescriptor(f, 'prototype').value, b);
assertTrue(Object.getOwnPropertyDescriptor(f, 'prototype').writable);

// Verify that the previous redefinition didn't screw up callbacks and
// the internal value still gets updated.
var c = { foo: 'other' };
f.prototype = c;
assertSame(f.prototype, c);
assertSame(f.prototype.foo, 'other');
assertSame(new f().foo, 'other');
assertSame(Object.getPrototypeOf(new f()), c);
assertSame(Object.getOwnPropertyDescriptor(f, 'prototype').value, c);
assertTrue(Object.getOwnPropertyDescriptor(f, 'prototype').writable);

// Verify that 'prototype' can be redefined to contain a different value
// and have a different writability attribute at the same time.
var d = { foo: 'final' };
Object.defineProperty(f, 'prototype', { value: d, writable: false });
assertSame(f.prototype, d);
assertSame(f.prototype.foo, 'final');
assertSame(new f().foo, 'final');
assertSame(Object.getPrototypeOf(new f()), d);
assertSame(Object.getOwnPropertyDescriptor(f, 'prototype').value, d);
assertFalse(Object.getOwnPropertyDescriptor(f, 'prototype').writable);

// Verify that non-writability of redefined 'prototype' is respected.
assertThrows("'use strict'; f.prototype = {}");
assertThrows("Object.defineProperty(f, 'prototype', { value: {} })");

// Verify that non-configurability of other properties is respected, but
// non-writability is ignored by Object.defineProperty().
// name and length are configurable in ES6
Object.defineProperty(f, 'name', { value: {} });
Object.defineProperty(f, 'length', { value: {} });
assertThrows("Object.defineProperty(f, 'caller', { value: {} })");
assertThrows("Object.defineProperty(f, 'arguments', { value: {} })");