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 x = { foo: 'bar' };
f.prototype = x;
assertSame(f.prototype, x);
assertSame(f.prototype.foo, 'bar');
assertSame(new f().foo, 'bar');
assertSame(Object.getPrototypeOf(new f()), x);
assertSame(Object.getOwnPropertyDescriptor(f, 'prototype').value, x);

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

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

// Verify that non-writability of other properties is respected.
assertThrows("Object.defineProperty(f, 'name', { value: {} })");
assertThrows("Object.defineProperty(f, 'length', { value: {} })");
assertThrows("Object.defineProperty(f, 'caller', { value: {} })");
assertThrows("Object.defineProperty(f, 'arguments', { value: {} })");