v8/test/mjsunit/object-define-property.js

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// Tests the object.defineProperty method - ES 15.2.3.6

// Flags: --allow-natives-syntax

// Check that an exception is thrown when null is passed as object.
try {
  Object.defineProperty(null, null, null);
  assertTrue(false);
} catch (e) {
  assertTrue(/called on non-object/.test(e));
}

// Check that an exception is thrown when undefined is passed as object.
try {
  Object.defineProperty(undefined, undefined, undefined);
  assertTrue(false);
} catch (e) {
  assertTrue(/called on non-object/.test(e));
}

// Check that an exception is thrown when non-object is passed as object.
try {
  Object.defineProperty(0, "foo", undefined);
  assertTrue(false);
} catch (e) {
  assertTrue(/called on non-object/.test(e));
}

// Object.
var obj1 = {};

// Values.
var val1 = 0;
var val2 = 0;
var val3 = 0;

function setter1() {val1++; }
function getter1() {return val1; }

function setter2() {val2++; }
function getter2() {return val2; }

function setter3() {val3++; }
function getter3() {return val3; }


// Descriptors.
var emptyDesc = {};

var accessorConfigurable = { 
    set: setter1,
    get: getter1,
    configurable: true
};

var accessorNoConfigurable = {
    set: setter2,
    get: getter2,
    configurable: false 
};

var accessorOnlySet = {
  set: setter3,
  configurable: true
};

var accessorOnlyGet = {
  get: getter3,
  configurable: true
};

var accessorDefault = {set: function(){} };

var dataConfigurable = { value: 1000, configurable: true };

var dataNoConfigurable = { value: 2000, configurable: false };

var dataWritable = { value: 3000, writable: true};


// Check that we can't add property with undefined attributes.
try {
  Object.defineProperty(obj1, "foo", undefined);
  assertTrue(false);
} catch (e) {
  assertTrue(/must be an object/.test(e));
}

// Make sure that we can add a property with an empty descriptor and
// that it has the default descriptor values.
Object.defineProperty(obj1, "foo", emptyDesc);

// foo should be undefined as it has no get, set or value
assertEquals(undefined, obj1.foo);

// We should, however, be able to retrieve the propertydescriptor which should
// have all default values (according to 8.6.1).
var desc = Object.getOwnPropertyDescriptor(obj1, "foo");
assertFalse(desc.configurable);
assertFalse(desc.enumerable);
assertFalse(desc.writable);
assertEquals(desc.get, undefined);
assertEquals(desc.set, undefined);
assertEquals(desc.value, undefined);

// Make sure that getOwnPropertyDescriptor does not return a descriptor
// with default values if called with non existing property (otherwise
// the test above is invalid).
desc = Object.getOwnPropertyDescriptor(obj1, "bar");
assertEquals(desc, undefined);

// Make sure that foo can't be reset (as configurable is false).
try {
  Object.defineProperty(obj1, "foo", accessorConfigurable);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}


// Accessor properties

Object.defineProperty(obj1, "bar", accessorConfigurable);
desc = Object.getOwnPropertyDescriptor(obj1, "bar");
assertTrue(desc.configurable);
assertFalse(desc.enumerable);
assertEquals(desc.writable, undefined);
assertEquals(desc.get, accessorConfigurable.get);
assertEquals(desc.set, accessorConfigurable.set);
assertEquals(desc.value, undefined);
assertEquals(1, obj1.bar = 1);
assertEquals(1, val1);
assertEquals(1, obj1.bar = 1);
assertEquals(2, val1);
assertEquals(2, obj1.bar);

// Redefine bar with non configurable test
Object.defineProperty(obj1, "bar", accessorNoConfigurable);
desc = Object.getOwnPropertyDescriptor(obj1, "bar");
assertFalse(desc.configurable);
assertFalse(desc.enumerable);
assertEquals(desc.writable, undefined);
assertEquals(desc.get, accessorNoConfigurable.get);
assertEquals(desc.set, accessorNoConfigurable.set);
assertEquals(desc.value, undefined);
assertEquals(1, obj1.bar = 1);
assertEquals(2, val1);
assertEquals(1, val2);
assertEquals(1, obj1.bar = 1)
assertEquals(2, val1);
assertEquals(2, val2);
assertEquals(2, obj1.bar);

// Try to redefine bar again - should fail as configurable is false.
try {
  Object.defineProperty(obj1, "bar", accessorConfigurable);
  assertTrue(false);
} catch(e) {
  assertTrue(/Cannot redefine property/.test(e));
}

// Try to redefine bar again using the data descriptor - should fail.
try {
  Object.defineProperty(obj1, "bar", dataConfigurable);
  assertTrue(false);
} catch(e) {
  assertTrue(/Cannot redefine property/.test(e));
}

// Redefine using same descriptor - should succeed.
Object.defineProperty(obj1, "bar", accessorNoConfigurable);
desc = Object.getOwnPropertyDescriptor(obj1, "bar");
assertFalse(desc.configurable);
assertFalse(desc.enumerable);
assertEquals(desc.writable, undefined);
assertEquals(desc.get, accessorNoConfigurable.get);
assertEquals(desc.set, accessorNoConfigurable.set);
assertEquals(desc.value, undefined);
assertEquals(1, obj1.bar = 1);
assertEquals(2, val1);
assertEquals(3, val2);
assertEquals(1, obj1.bar = 1)
assertEquals(2, val1);
assertEquals(4, val2);
assertEquals(4, obj1.bar);

// Define an accessor that has only a setter.
Object.defineProperty(obj1, "setOnly", accessorOnlySet);
desc = Object.getOwnPropertyDescriptor(obj1, "setOnly");
assertTrue(desc.configurable);
assertFalse(desc.enumerable);
assertEquals(desc.set, accessorOnlySet.set);
assertEquals(desc.writable, undefined);
assertEquals(desc.value, undefined);
assertEquals(desc.get, undefined);
assertEquals(1, obj1.setOnly = 1);
assertEquals(1, val3);

// Add a getter - should not touch the setter.
Object.defineProperty(obj1, "setOnly", accessorOnlyGet);
desc = Object.getOwnPropertyDescriptor(obj1, "setOnly");
assertTrue(desc.configurable);
assertFalse(desc.enumerable);
assertEquals(desc.get, accessorOnlyGet.get);
assertEquals(desc.set, accessorOnlySet.set);
assertEquals(desc.writable, undefined);
assertEquals(desc.value, undefined);
assertEquals(1, obj1.setOnly = 1);
assertEquals(2, val3);

// The above should also work if redefining just a getter or setter on 
// an existing property with both a getter and a setter.
Object.defineProperty(obj1, "both", accessorConfigurable);

Object.defineProperty(obj1, "both", accessorOnlySet);
desc = Object.getOwnPropertyDescriptor(obj1, "both");
assertTrue(desc.configurable);
assertFalse(desc.enumerable);
assertEquals(desc.set, accessorOnlySet.set);
assertEquals(desc.get, accessorConfigurable.get);
assertEquals(desc.writable, undefined);
assertEquals(desc.value, undefined);
assertEquals(1, obj1.both = 1);
assertEquals(3, val3);


// Data properties

Object.defineProperty(obj1, "foobar", dataConfigurable);
desc = Object.getOwnPropertyDescriptor(obj1, "foobar");
assertEquals(obj1.foobar, 1000);
assertEquals(desc.value, 1000);
assertTrue(desc.configurable);
assertFalse(desc.writable);
assertFalse(desc.enumerable);
assertEquals(desc.get, undefined);
assertEquals(desc.set, undefined);
//Try writing to non writable attribute - should remain 1000
obj1.foobar = 1001;
assertEquals(obj1.foobar, 1000);


// Redefine to writable descriptor - now writing to foobar should be allowed.
Object.defineProperty(obj1, "foobar", dataWritable);
desc = Object.getOwnPropertyDescriptor(obj1, "foobar");
assertEquals(obj1.foobar, 3000);
assertEquals(desc.value, 3000);
// Note that since dataWritable does not define configurable the configurable
// setting from the redefined property (in this case true) is used.
assertTrue(desc.configurable);
assertTrue(desc.writable);
assertFalse(desc.enumerable);
assertEquals(desc.get, undefined);
assertEquals(desc.set, undefined);
// Writing to the property should now be allowed
obj1.foobar = 1001;
assertEquals(obj1.foobar, 1001);


// Redefine with non configurable data property.
Object.defineProperty(obj1, "foobar", dataNoConfigurable);
desc = Object.getOwnPropertyDescriptor(obj1, "foobar");
assertEquals(obj1.foobar, 2000);
assertEquals(desc.value, 2000);
assertFalse(desc.configurable);
assertTrue(desc.writable);
assertFalse(desc.enumerable);
assertEquals(desc.get, undefined);
assertEquals(desc.set, undefined);

// Try redefine again - shold fail because configurable is now false.
try {
  Object.defineProperty(obj1, "foobar", dataConfigurable);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}

// Try redefine again with accessor property - shold also fail.
try {
  Object.defineProperty(obj1, "foobar", dataConfigurable);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}


// Redifine with the same descriptor - should succeed (step 6).
Object.defineProperty(obj1, "foobar", dataNoConfigurable);
desc = Object.getOwnPropertyDescriptor(obj1, "foobar");
assertEquals(obj1.foobar, 2000);
assertEquals(desc.value, 2000);
assertFalse(desc.configurable);
assertTrue(desc.writable);
assertFalse(desc.enumerable);
assertEquals(desc.get, undefined);
assertEquals(desc.set, undefined);


// New object
var obj2 = {};

// Make accessor - redefine to data
Object.defineProperty(obj2, "foo", accessorConfigurable);

// Redefine to data property
Object.defineProperty(obj2, "foo", dataConfigurable);
desc = Object.getOwnPropertyDescriptor(obj2, "foo");
assertEquals(obj2.foo, 1000);
assertEquals(desc.value, 1000);
assertTrue(desc.configurable);
assertFalse(desc.writable);
assertFalse(desc.enumerable);
assertEquals(desc.get, undefined);
assertEquals(desc.set, undefined);


// Redefine back to accessor
Object.defineProperty(obj2, "foo", accessorConfigurable);
desc = Object.getOwnPropertyDescriptor(obj2, "foo");
assertTrue(desc.configurable);
assertFalse(desc.enumerable);
assertEquals(desc.writable, undefined);
assertEquals(desc.get, accessorConfigurable.get);
assertEquals(desc.set, accessorConfigurable.set);
assertEquals(desc.value, undefined);
assertEquals(1, obj2.foo = 1);
assertEquals(3, val1);
assertEquals(4, val2);
assertEquals(3, obj2.foo);

// Make data - redefine to accessor
Object.defineProperty(obj2, "bar", dataConfigurable)

// Redefine to accessor property
Object.defineProperty(obj2, "bar", accessorConfigurable);
desc = Object.getOwnPropertyDescriptor(obj2, "bar");
assertTrue(desc.configurable);
assertFalse(desc.enumerable);
assertEquals(desc.writable, undefined);
assertEquals(desc.get, accessorConfigurable.get);
assertEquals(desc.set, accessorConfigurable.set);
assertEquals(desc.value, undefined);
assertEquals(1, obj2.bar = 1);
assertEquals(4, val1);
assertEquals(4, val2);
assertEquals(4, obj2.foo);

// Redefine back to data property
Object.defineProperty(obj2, "bar", dataConfigurable);
desc = Object.getOwnPropertyDescriptor(obj2, "bar");
assertEquals(obj2.bar, 1000);
assertEquals(desc.value, 1000);
assertTrue(desc.configurable);
assertFalse(desc.writable);
assertFalse(desc.enumerable);
assertEquals(desc.get, undefined);
assertEquals(desc.set, undefined);


// Redefinition of an accessor defined using __defineGetter__ and 
// __defineSetter__.
function get(){return this.x}
function set(x){this.x=x};

var obj3 = {x:1000};
obj3.__defineGetter__("foo", get);
obj3.__defineSetter__("foo", set);

desc = Object.getOwnPropertyDescriptor(obj3, "foo");
assertTrue(desc.configurable);
assertTrue(desc.enumerable);
assertEquals(desc.writable, undefined);
assertEquals(desc.get, get);
assertEquals(desc.set, set);
assertEquals(desc.value, undefined);
assertEquals(1, obj3.foo = 1);
assertEquals(1, obj3.x);
assertEquals(1, obj3.foo);

// Redefine to accessor property (non configurable) - note that enumerable
// which we do not redefine should remain the same (true).
Object.defineProperty(obj3, "foo", accessorNoConfigurable);
desc = Object.getOwnPropertyDescriptor(obj3, "foo");
assertFalse(desc.configurable);
assertTrue(desc.enumerable);
assertEquals(desc.writable, undefined);
assertEquals(desc.get, accessorNoConfigurable.get);
assertEquals(desc.set, accessorNoConfigurable.set);
assertEquals(desc.value, undefined);
assertEquals(1, obj3.foo = 1);
assertEquals(5, val2);
assertEquals(5, obj3.foo);


obj3.__defineGetter__("bar", get);
obj3.__defineSetter__("bar", set);


// Redefine back to data property
Object.defineProperty(obj3, "bar", dataConfigurable);
desc = Object.getOwnPropertyDescriptor(obj3, "bar");
assertEquals(obj3.bar, 1000);
assertEquals(desc.value, 1000);
assertTrue(desc.configurable);
assertFalse(desc.writable);
assertTrue(desc.enumerable);
assertEquals(desc.get, undefined);
assertEquals(desc.set, undefined);


var obj4 = {};
var func = function (){return 42;};
obj4.bar = func;
assertEquals(42, obj4.bar());

Object.defineProperty(obj4, "bar", accessorConfigurable);
desc = Object.getOwnPropertyDescriptor(obj4, "bar");
assertTrue(desc.configurable);
assertTrue(desc.enumerable);
assertEquals(desc.writable, undefined);
assertEquals(desc.get, accessorConfigurable.get);
assertEquals(desc.set, accessorConfigurable.set);
assertEquals(desc.value, undefined);
assertEquals(1, obj4.bar = 1);
assertEquals(5, val1);
assertEquals(5, obj4.bar);

// Make sure an error is thrown when trying to access to redefined function.
try {
  obj4.bar();
  assertTrue(false);
} catch (e) {
  assertTrue(/is not a function/.test(e));
}


// Test runtime calls to DefineOrRedefineDataProperty and
// DefineOrRedefineAccessorProperty - make sure we don't 
// crash.
try {
  %DefineOrRedefineAccessorProperty(0, 0, 0, 0, 0);
} catch (e) {
  assertTrue(/illegal access/.test(e));
}

try {
  %DefineOrRedefineDataProperty(0, 0, 0, 0);
} catch (e) {
  assertTrue(/illegal access/.test(e));
}

try {
  %DefineOrRedefineDataProperty(null, null, null, null);
} catch (e) {
  assertTrue(/illegal access/.test(e));
}

try {
  %DefineOrRedefineAccessorProperty(null, null, null, null, null);
} catch (e) {
  assertTrue(/illegal access/.test(e));
}

try {
  %DefineOrRedefineDataProperty({}, null, null, null);
} catch (e) {
  assertTrue(/illegal access/.test(e));
}

// Defining properties null should fail even when we have
// other allowed values
try {
  %DefineOrRedefineAccessorProperty(null, 'foo', 0, func, 0);
} catch (e) {
  assertTrue(/illegal access/.test(e));
}

try {
  %DefineOrRedefineDataProperty(null, 'foo', 0, 0);
} catch (e) {
  assertTrue(/illegal access/.test(e));
}

// Test that all possible differences in step 6 in DefineOwnProperty are
// exercised, i.e., any difference in the given property descriptor and the
// existing properties should not return true, but throw an error if the
// existing configurable property is false. 

var obj5 = {};
// Enumerable will default to false.
Object.defineProperty(obj5, 'foo', accessorNoConfigurable);
desc = Object.getOwnPropertyDescriptor(obj5, 'foo');
// First, test that we are actually allowed to set the accessor if all
// values are of the descriptor are the same as the existing one.
Object.defineProperty(obj5, 'foo', accessorNoConfigurable);

// Different setter.
var descDifferent = {
  configurable:false,
  enumerable:false,
  set: setter1,
  get: getter2
};

try {
  Object.defineProperty(obj5, 'foo', descDifferent);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}

// Different getter.
descDifferent = {
  configurable:false,
  enumerable:false,
  set: setter2,
  get: getter1
};

try {
  Object.defineProperty(obj5, 'foo', descDifferent);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}

// Different enumerable.
descDifferent = {
  configurable:false,
  enumerable:true,
  set: setter2,
  get: getter2
};

try {
  Object.defineProperty(obj5, 'foo', descDifferent);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}

// Different configurable.
descDifferent = {
  configurable:false,
  enumerable:true,
  set: setter2,
  get: getter2
};

try {
  Object.defineProperty(obj5, 'foo', descDifferent);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}

// No difference.
descDifferent = {
  configurable:false,
  enumerable:false,
  set: setter2,
  get: getter2
};
// Make sure we can still redefine if all properties are the same.
Object.defineProperty(obj5, 'foo', descDifferent);

// Make sure that obj5 still holds the original values.
desc = Object.getOwnPropertyDescriptor(obj5, 'foo');
assertEquals(desc.get, getter2);
assertEquals(desc.set, setter2);
assertFalse(desc.enumerable);
assertFalse(desc.configurable);


// Also exercise step 6 on data property, writable and enumerable
// defaults to false.
Object.defineProperty(obj5, 'bar', dataNoConfigurable);

// Test that redefinition with the same property descriptor is possible
Object.defineProperty(obj5, 'bar', dataNoConfigurable);

// Different value.
descDifferent = {
  configurable:false,
  enumerable:false,
  writable: false,
  value: 1999
};

try {
  Object.defineProperty(obj5, 'bar', descDifferent);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}

// Different writable.
descDifferent = {
  configurable:false,
  enumerable:false,
  writable: true,
  value: 2000
};

try {
  Object.defineProperty(obj5, 'bar', descDifferent);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}


// Different enumerable.
descDifferent = {
  configurable:false,
  enumerable:true ,
  writable:false,
  value: 2000
};

try {
  Object.defineProperty(obj5, 'bar', descDifferent);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}


// Different configurable.
descDifferent = {
  configurable:true,
  enumerable:false,
  writable:false,
  value: 2000
};

try {
  Object.defineProperty(obj5, 'bar', descDifferent);
  assertTrue(false);
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}

// No difference.
descDifferent = {
  configurable:false,
  enumerable:false,
  writable:false,
  value:2000
};
// Make sure we can still redefine if all properties are the same.
Object.defineProperty(obj5, 'bar', descDifferent);

// Make sure that obj5 still holds the original values.
desc = Object.getOwnPropertyDescriptor(obj5, 'bar');
assertEquals(desc.value, 2000);
assertFalse(desc.writable);
assertFalse(desc.enumerable);
assertFalse(desc.configurable);


// Make sure that we can't overwrite +0 with -0 and vice versa.
var descMinusZero = {value: -0, configurable: false};
var descPlusZero = {value: +0, configurable: false};

Object.defineProperty(obj5, 'minuszero', descMinusZero);

// Make sure we can redefine with -0.
Object.defineProperty(obj5, 'minuszero', descMinusZero);

try {
  Object.defineProperty(obj5, 'minuszero', descPlusZero);
  assertUnreachable();
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}


Object.defineProperty(obj5, 'pluszero', descPlusZero);

// Make sure we can redefine with +0.
Object.defineProperty(obj5, 'pluszero', descPlusZero);

try {
  Object.defineProperty(obj5, 'pluszero', descMinusZero);
  assertUnreachable();
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}


var obj6 = {};
obj6[1] = 'foo';
obj6[2] = 'bar';
obj6[3] = '42';
obj6[4] = '43';
obj6[5] = '44';

var descElement = { value: 'foobar' };
var descElementNonConfigurable = { value: 'barfoo', configurable: false };
var descElementNonWritable = { value: 'foofoo', writable: false };
var descElementNonEnumerable = { value: 'barbar', enumerable: false };
var descElementAllFalse = { value: 'foofalse', 
                            configurable: false,
                            writable: false,
                            enumerable: false };


// Redefine existing property.
Object.defineProperty(obj6, '1', descElement);
desc = Object.getOwnPropertyDescriptor(obj6, '1');
assertEquals(desc.value, 'foobar');
assertTrue(desc.writable);
assertTrue(desc.enumerable);
assertTrue(desc.configurable);

// Redefine existing property with configurable: false.
Object.defineProperty(obj6, '2', descElementNonConfigurable);
desc = Object.getOwnPropertyDescriptor(obj6, '2');
assertEquals(desc.value, 'barfoo');
assertTrue(desc.writable);
assertTrue(desc.enumerable);
assertFalse(desc.configurable);

// Ensure that we can't overwrite the non configurable element.
try {
  Object.defineProperty(obj6, '2', descElement);
  assertUnreachable();
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}

Object.defineProperty(obj6, '3', descElementNonWritable);
desc = Object.getOwnPropertyDescriptor(obj6, '3');
assertEquals(desc.value, 'foofoo');
assertFalse(desc.writable);
assertTrue(desc.enumerable);
assertTrue(desc.configurable);

// Redefine existing property with configurable: false.
Object.defineProperty(obj6, '4', descElementNonEnumerable);
desc = Object.getOwnPropertyDescriptor(obj6, '4');
assertEquals(desc.value, 'barbar');
assertTrue(desc.writable);
assertFalse(desc.enumerable);
assertTrue(desc.configurable);

// Redefine existing property with configurable: false.
Object.defineProperty(obj6, '5', descElementAllFalse);
desc = Object.getOwnPropertyDescriptor(obj6, '5');
assertEquals(desc.value, 'foofalse');
assertFalse(desc.writable);
assertFalse(desc.enumerable);
assertFalse(desc.configurable);

// Define non existing property - all attributes should default to false.
Object.defineProperty(obj6, '15', descElement);
desc = Object.getOwnPropertyDescriptor(obj6, '15');
assertEquals(desc.value, 'foobar');
assertFalse(desc.writable);
assertFalse(desc.enumerable);
assertFalse(desc.configurable);

// Make sure that we can't redefine using direct access.
obj6[15] ='overwrite';
assertEquals(obj6[15],'foobar'); 


// Repeat the above tests on an array.
var arr = new Array();
arr[1] = 'foo';
arr[2] = 'bar';
arr[3] = '42';
arr[4] = '43';
arr[5] = '44';

var descElement = { value: 'foobar' };
var descElementNonConfigurable = { value: 'barfoo', configurable: false };
var descElementNonWritable = { value: 'foofoo', writable: false };
var descElementNonEnumerable = { value: 'barbar', enumerable: false };
var descElementAllFalse = { value: 'foofalse', 
                            configurable: false,
                            writable: false,
                            enumerable: false };


// Redefine existing property.
Object.defineProperty(arr, '1', descElement);
desc = Object.getOwnPropertyDescriptor(arr, '1');
assertEquals(desc.value, 'foobar');
assertTrue(desc.writable);
assertTrue(desc.enumerable);
assertTrue(desc.configurable);

// Redefine existing property with configurable: false.
Object.defineProperty(arr, '2', descElementNonConfigurable);
desc = Object.getOwnPropertyDescriptor(arr, '2');
assertEquals(desc.value, 'barfoo');
assertTrue(desc.writable);
assertTrue(desc.enumerable);
assertFalse(desc.configurable);

// Ensure that we can't overwrite the non configurable element.
try {
  Object.defineProperty(arr, '2', descElement);
  assertUnreachable();
} catch (e) {
  assertTrue(/Cannot redefine property/.test(e));
}

Object.defineProperty(arr, '3', descElementNonWritable);
desc = Object.getOwnPropertyDescriptor(arr, '3');
assertEquals(desc.value, 'foofoo');
assertFalse(desc.writable);
assertTrue(desc.enumerable);
assertTrue(desc.configurable);

// Redefine existing property with configurable: false.
Object.defineProperty(arr, '4', descElementNonEnumerable);
desc = Object.getOwnPropertyDescriptor(arr, '4');
assertEquals(desc.value, 'barbar');
assertTrue(desc.writable);
assertFalse(desc.enumerable);
assertTrue(desc.configurable);

// Redefine existing property with configurable: false.
Object.defineProperty(arr, '5', descElementAllFalse);
desc = Object.getOwnPropertyDescriptor(arr, '5');
assertEquals(desc.value, 'foofalse');
assertFalse(desc.writable);
assertFalse(desc.enumerable);
assertFalse(desc.configurable);

// Define non existing property - all attributes should default to false.
Object.defineProperty(arr, '15', descElement);
desc = Object.getOwnPropertyDescriptor(arr, '15');
assertEquals(desc.value, 'foobar');
assertFalse(desc.writable);
assertFalse(desc.enumerable);
assertFalse(desc.configurable);