v8/test/mjsunit/object-freeze.js

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// Tests the Object.freeze and Object.isFrozen methods - ES 19.1.2.5 and
// ES 19.1.2.12

// Flags: --allow-natives-syntax

// Test that we return obj if non-object is passed as argument
var non_objects = new Array(undefined, null, 1, -1, 0, 42.43, Symbol("test"));
for (var key in non_objects) {
  assertSame(non_objects[key], Object.freeze(non_objects[key]));
}

// Test that isFrozen always returns true for non-objects
for (var key in non_objects) {
  assertTrue(Object.isFrozen(non_objects[key]));
}

// Test normal data properties.
var obj = { x: 42, z: 'foobar' };
var desc = Object.getOwnPropertyDescriptor(obj, 'x');
assertTrue(desc.writable);
assertTrue(desc.configurable);
assertEquals(42, desc.value);

desc = Object.getOwnPropertyDescriptor(obj, 'z');
assertTrue(desc.writable);
assertTrue(desc.configurable);
assertEquals('foobar', desc.value);

assertTrue(Object.isExtensible(obj));
assertFalse(Object.isFrozen(obj));

Object.freeze(obj);

// Make sure we are no longer extensible.
assertFalse(Object.isExtensible(obj));
assertTrue(Object.isFrozen(obj));

obj.foo = 42;
assertEquals(obj.foo, undefined);

desc = Object.getOwnPropertyDescriptor(obj, 'x');
assertFalse(desc.writable);
assertFalse(desc.configurable);
assertEquals(42, desc.value);

desc = Object.getOwnPropertyDescriptor(obj, 'z');
assertFalse(desc.writable);
assertFalse(desc.configurable);
assertEquals("foobar", desc.value);

// Make sure that even if we try overwrite a value that is not writable, it is
// not changed.
obj.x = "tete";
assertEquals(42, obj.x);
obj.x = { get: function() {return 43}, set: function() {} };
assertEquals(42, obj.x);

// Test on accessors.
var obj2 = {};
function get() { return 43; };
function set() {};
Object.defineProperty(obj2, 'x', { get: get, set: set, configurable: true });

desc = Object.getOwnPropertyDescriptor(obj2, 'x');
assertTrue(desc.configurable);
assertEquals(undefined, desc.value);
assertEquals(set, desc.set);
assertEquals(get, desc.get);

assertTrue(Object.isExtensible(obj2));
assertFalse(Object.isFrozen(obj2));
Object.freeze(obj2);
assertTrue(Object.isFrozen(obj2));
assertFalse(Object.isExtensible(obj2));

desc = Object.getOwnPropertyDescriptor(obj2, 'x');
assertFalse(desc.configurable);
assertEquals(undefined, desc.value);
assertEquals(set, desc.set);
assertEquals(get, desc.get);

obj2.foo = 42;
assertEquals(obj2.foo, undefined);


// Test freeze on arrays.
var arr = new Array(42,43);

desc = Object.getOwnPropertyDescriptor(arr, '0');
assertTrue(desc.configurable);
assertTrue(desc.writable);
assertEquals(42, desc.value);

desc = Object.getOwnPropertyDescriptor(arr, '1');
assertTrue(desc.configurable);
assertTrue(desc.writable);
assertEquals(43, desc.value);

assertTrue(Object.isExtensible(arr));
assertFalse(Object.isFrozen(arr));
Object.freeze(arr);
assertTrue(Object.isFrozen(arr));
assertFalse(Object.isExtensible(arr));

desc = Object.getOwnPropertyDescriptor(arr, '0');
assertFalse(desc.configurable);
assertFalse(desc.writable);
assertEquals(42, desc.value);

desc = Object.getOwnPropertyDescriptor(arr, '1');
assertFalse(desc.configurable);
assertFalse(desc.writable);
assertEquals(43, desc.value);

arr[0] = 'foo';

assertEquals(arr[0], 42);


// Test that isFrozen return the correct value even if configurable has been set
// to false on all properties manually and the extensible flag has also been set
// to false manually.
var obj3 = { x: 42, y: 'foo' };

assertFalse(Object.isFrozen(obj3));

Object.defineProperty(obj3, 'x', {configurable: false, writable: false});
Object.defineProperty(obj3, 'y', {configurable: false, writable: false});
Object.preventExtensions(obj3);

assertTrue(Object.isFrozen(obj3));


// Make sure that an object that has only non-configurable, but one
// writable property, is not classified as frozen.
var obj4 = {};
Object.defineProperty(obj4, 'x', {configurable: false, writable: true});
Object.defineProperty(obj4, 'y', {configurable: false, writable: false});
Object.preventExtensions(obj4);

assertFalse(Object.isFrozen(obj4));

// Make sure that an object that has only non-writable, but one
// configurable property, is not classified as frozen.
var obj5 = {};
Object.defineProperty(obj5, 'x', {configurable: true, writable: false});
Object.defineProperty(obj5, 'y', {configurable: false, writable: false});
Object.preventExtensions(obj5);

assertFalse(Object.isFrozen(obj5));

// Make sure that Object.freeze returns the frozen object.
var obj6 = {}
assertTrue(obj6 === Object.freeze(obj6))

// Test that the enumerable attribute is unperturbed by freezing.
obj = { x: 42, y: 'foo' };
Object.defineProperty(obj, 'y', {enumerable: false});
Object.freeze(obj);
assertTrue(Object.isFrozen(obj));
desc = Object.getOwnPropertyDescriptor(obj, 'x');
assertTrue(desc.enumerable);
desc = Object.getOwnPropertyDescriptor(obj, 'y');
assertFalse(desc.enumerable);

// Fast properties should remain fast
obj = { x: 42, y: 'foo' };
assertTrue(%HasFastProperties(obj));
Object.freeze(obj);
assertTrue(Object.isFrozen(obj));
assertTrue(%HasFastProperties(obj));

// Frozen objects should share maps where possible
obj = { prop1: 1, prop2: 2 };
obj2 = { prop1: 3, prop2: 4 };
assertTrue(%HaveSameMap(obj, obj2));
Object.freeze(obj);
Object.freeze(obj2);
assertTrue(Object.isFrozen(obj));
assertTrue(Object.isFrozen(obj2));
assertTrue(%HaveSameMap(obj, obj2));

// Frozen objects should share maps even when they have elements
obj = { prop1: 1, prop2: 2, 75: 'foo' };
obj2 = { prop1: 3, prop2: 4, 150: 'bar' };
assertTrue(%HaveSameMap(obj, obj2));
Object.freeze(obj);
Object.freeze(obj2);
assertTrue(Object.isFrozen(obj));
assertTrue(Object.isFrozen(obj2));
assertTrue(%HaveSameMap(obj, obj2));

// Setting elements after freezing should not be allowed
obj = { prop: 'thing' };
Object.freeze(obj);
assertTrue(Object.isFrozen(obj));
obj[0] = 'hello';
assertFalse(obj.hasOwnProperty(0));

// Freezing an object in dictionary mode should work
// Also testing that getter/setter properties work after freezing
obj = { };
for (var i = 0; i < 100; ++i) {
  obj['x' + i] = i;
}
var accessorDidRun = false;
Object.defineProperty(obj, 'accessor', {
  get: function() { return 42 },
  set: function() { accessorDidRun = true },
  configurable: true,
  enumerable: true
});

assertFalse(%HasFastProperties(obj));
Object.freeze(obj);
assertFalse(%HasFastProperties(obj));
assertTrue(Object.isFrozen(obj));
assertFalse(Object.isExtensible(obj));
for (var i = 0; i < 100; ++i) {
  desc = Object.getOwnPropertyDescriptor(obj, 'x' + i);
  assertFalse(desc.writable);
  assertFalse(desc.configurable);
}
assertEquals(42, obj.accessor);
assertFalse(accessorDidRun);
obj.accessor = 'ignored value';
assertTrue(accessorDidRun);

// Freezing arguments should work
var func = function(arg) {
  Object.freeze(arguments);
  assertTrue(Object.isFrozen(arguments));
};
func('hello', 'world');
func('goodbye', 'world');

// Freezing sparse arrays
var sparseArr = [0, 1];
sparseArr[10000] = 10000;
Object.freeze(sparseArr);
assertTrue(Object.isFrozen(sparseArr));

// Accessors on fast object should behavior properly after freezing
obj = {};
Object.defineProperty(obj, 'accessor', {
  get: function() { return 42 },
  set: function() { accessorDidRun = true },
  configurable: true,
  enumerable: true
});
assertTrue(%HasFastProperties(obj));
Object.freeze(obj);
assertTrue(Object.isFrozen(obj));
assertTrue(%HasFastProperties(obj));
assertEquals(42, obj.accessor);
accessorDidRun = false;
obj.accessor = 'ignored value';
assertTrue(accessorDidRun);

// Test for regression in mixed accessor/data property objects.
// The strict function is one such object.
assertTrue(Object.isFrozen(Object.freeze(function(){"use strict";})));

// Also test a simpler case
obj = {};
Object.defineProperty(obj, 'accessor2', {
  get: function() { return 42 },
  set: function() { accessorDidRun = true },
  configurable: true,
  enumerable: true
});
obj.data = 'foo';
assertTrue(%HasFastProperties(obj));
Object.freeze(obj);
assertTrue(%HasFastProperties(obj));
assertTrue(Object.isFrozen(obj));

// Test array built-in functions with freeze.
obj = [1,2,3];
Object.freeze(obj);
// if frozen implies sealed, then the tests in object-seal.js are mostly
// sufficient.
assertTrue(Object.isSealed(obj));

// Verify that the length can't be written by builtins.
assertThrows(function() { obj.push(); }, TypeError);
assertThrows(function() { obj.unshift(); }, TypeError);
assertThrows(function() { obj.splice(0,0); }, TypeError);
assertTrue(Object.isFrozen(obj));

// Verify that an item can't be changed with splice.
assertThrows(function() { obj.splice(0,1,1); }, TypeError);
assertTrue(Object.isFrozen(obj));

// Verify that unshift() with no arguments will fail if it reifies from
// the prototype into the object.
obj = [1,,3];
obj.__proto__[1] = 1;
assertEquals(1, obj[1]);
Object.freeze(obj);
assertThrows(function() { obj.unshift(); }, TypeError);

// Sealing and then Freezing should do the right thing.
var obj = { foo: 'bar', 0: 'element' };
Object.seal(obj);
assertTrue(Object.isSealed(obj));
assertFalse(Object.isFrozen(obj));
Object.freeze(obj);
assertTrue(Object.isSealed(obj));
assertTrue(Object.isFrozen(obj));


(function propertiesOfFrozenObjectNotFrozen() {
  function Frozen() {}
  Object.freeze(Frozen);
  assertDoesNotThrow(function() { return new Frozen(); });
  Frozen.prototype.prototypeExists = true;
  assertTrue((new Frozen()).prototypeExists);
})();


(function frozenPrototypePreventsPUT() {
  // A read-only property on the prototype should prevent a [[Put]] .
  function Constructor() {}
  Constructor.prototype.foo = 1;
  Object.freeze(Constructor.prototype);
  var obj = new Constructor();
  obj.foo = 2;
  assertSame(1, obj.foo);
})();


(function frozenFunctionSloppy() {
  // Check that freezing a function works correctly.
  var func = Object.freeze(function foo(){});
  assertTrue(Object.isFrozen(func));
  func.prototype = 42;
  assertFalse(func.prototype === 42);
  assertFalse(Object.getOwnPropertyDescriptor(func, "prototype").writable);
})();


(function frozenFunctionStrict() {
  // Check that freezing a strict function works correctly.
  var func = Object.freeze(function foo(){ "use strict"; });
  assertTrue(Object.isFrozen(func));
  func.prototype = 42;
  assertFalse(func.prototype === 42);
  assertFalse(Object.getOwnPropertyDescriptor(func, "prototype").writable);
})();


(function frozenArrayObject() {
  // Check that freezing array objects works correctly.
  var array = Object.freeze([0,1,2]);
  assertTrue(Object.isFrozen(array));
  array[0] = 3;
  assertEquals(0, array[0]);
  assertFalse(Object.getOwnPropertyDescriptor(array, "length").writable);
})();


(function frozenArgumentsObject() {
  // Check that freezing arguments objects works correctly.
  var args = Object.freeze((function(){ return arguments; })(0,1,2));
  assertTrue(Object.isFrozen(args));
  args[0] = 3;
  assertEquals(0, args[0]);
  assertFalse(Object.getOwnPropertyDescriptor(args, "length").writable);
  assertFalse(Object.getOwnPropertyDescriptor(args, "callee").writable);
})();

// Test packed element array built-in functions with freeze.
function testPackedFrozenArray1(obj) {
  assertTrue(Object.isSealed(obj));
  // Verify that the value can't be written
  obj1 = new Array(...obj);
  var length = obj.length;
  for (var i = 0; i < length-1; i++) {
    obj[i] = 'new';
    assertEquals(obj1[i], obj[i]);
  }
  // for symbol we cannot compare directly
  assertTrue(typeof obj[length-1] == 'symbol');

  // Verify that the length can't be written by builtins.
  assertTrue(Array.isArray(obj));
  assertThrows(function() { obj.pop(); }, TypeError);
  assertThrows(function() { obj.push(); }, TypeError);
  assertThrows(function() { obj.shift(); }, TypeError);
  assertThrows(function() { obj.unshift(); }, TypeError);
  assertThrows(function() { obj.copyWithin(0,0); }, TypeError);
  assertThrows(function() { obj.fill(0); }, TypeError);
  assertThrows(function() { obj.reverse(); }, TypeError);
  assertThrows(function() { obj.sort(); }, TypeError);
  assertThrows(function() { obj.splice(0); }, TypeError);
  assertThrows(function() { obj.splice(0, 0); }, TypeError);
  assertTrue(Object.isFrozen(obj));

  // Verify search, filter, iterator
  assertEquals(obj.lastIndexOf(1), 2);
  assertEquals(obj.indexOf('a'), 4);
  assertEquals(obj.indexOf(undefined), 0);
  assertFalse(obj.includes(Symbol("test")));
  assertTrue(obj.includes(undefined));
  assertFalse(obj.includes(NaN));
  assertTrue(obj.includes());
  assertEquals(obj.find(x => x==0), undefined);
  assertEquals(obj.findIndex(x => x=='a'), 4);
  assertTrue(obj.some(x => typeof x == 'symbol'));
  assertFalse(obj.every(x => x == -1));
  var filteredArray = obj.filter(e => typeof e == "symbol");
  assertEquals(filteredArray.length, 1);
  assertEquals(obj.map(x => x), obj);
  var countPositiveNumber = 0;
  obj.forEach(function(item, index) {
    if (item === 1) {
      countPositiveNumber++;
      assertEquals(index, 2);
    }
  });
  assertEquals(countPositiveNumber, 1);
  assertEquals(obj.length, obj.concat([]).length);
  var iterator = obj.values();
  assertEquals(iterator.next().value, undefined);
  assertEquals(iterator.next().value, null);
  var iterator = obj.keys();
  assertEquals(iterator.next().value, 0);
  assertEquals(iterator.next().value, 1);
  var iterator = obj.entries();
  assertEquals(iterator.next().value, [0, undefined]);
  assertEquals(iterator.next().value, [1, null]);
}

obj = new Array(undefined, null, 1, -1, 'a', Symbol("test"));
assertTrue(%HasPackedElements(obj));
Object.freeze(obj);
testPackedFrozenArray1(obj);

// Verify change from sealed to frozen
obj = new Array(undefined, null, 1, -1, 'a', Symbol("test"));
assertTrue(%HasPackedElements(obj));
Object.seal(obj);
Object.freeze(obj);
assertTrue(Object.isSealed(obj));
testPackedFrozenArray1(obj);

// Verify change from non-extensible to frozen
obj = new Array(undefined, null, 1, -1, 'a', Symbol("test"));
assertTrue(%HasPackedElements(obj));
Object.preventExtensions(obj);
Object.freeze(obj);
assertTrue(Object.isSealed(obj));
testPackedFrozenArray1(obj);

// Verify flat, map, slice, flatMap, join, reduce, reduceRight for frozen packed array
function testPackedFrozenArray2(arr) {
  assertTrue(Object.isFrozen(arr));
  assertTrue(Array.isArray(arr));
  assertEquals(arr.map(x => [x]), [['a'], ['b'], ['c']]);
  assertEquals(arr.flatMap(x => [x]), arr);
  assertEquals(arr.flat(), arr);
  assertEquals(arr.join('-'), "a-b-c");
  const reducer = (accumulator, currentValue) => accumulator + currentValue;
  assertEquals(arr.reduce(reducer), "abc");
  assertEquals(arr.reduceRight(reducer), "cba");
  assertEquals(arr.slice(0, 1), ['a']);
}
var arr1 = new Array('a', 'b', 'c');
assertTrue(%HasPackedElements(arr1));
Object.freeze(arr1);
testPackedFrozenArray2(arr1);

// Verify change from sealed to frozen
var arr2 = new Array('a', 'b', 'c');
assertTrue(%HasPackedElements(arr2));
Object.seal(arr2);
Object.freeze(arr2);
testPackedFrozenArray2(arr2);

// Verify change from non-extensible to frozen
var arr2 = new Array('a', 'b', 'c');
assertTrue(%HasPackedElements(arr2));
Object.preventExtensions(arr2);
Object.freeze(arr2);
testPackedFrozenArray2(arr2);

// Verify that repeatedly attemping to freeze a typed array fails
var typedArray = new Uint8Array(10);
assertThrows(() => { Object.freeze(typedArray); }, TypeError);
assertFalse(Object.isFrozen(typedArray));
assertThrows(() => { Object.freeze(typedArray); }, TypeError);
assertFalse(Object.isFrozen(typedArray));

// Verify that freezing an empty typed array works
var typedArray = new Uint8Array(0);
Object.freeze(typedArray);
assertTrue(Object.isFrozen(typedArray));

// Test regression with Object.defineProperty
var obj = [];
obj.propertyA = 42;
obj[0] = true;
Object.freeze(obj);
assertThrows(function() {
  Object.defineProperty(obj, 'propertyA', {
    value: obj,
  });
}, TypeError);
assertEquals(42, obj.propertyA);
assertThrows(function() {
  Object.defineProperty(obj, 'propertyA', {
    value: obj,
    writable: false,
  });
}, TypeError);
assertDoesNotThrow(function() {obj.propertyA = 2;});
assertEquals(obj.propertyA, 42);
assertThrows(function() {
  Object.defineProperty(obj, 'abc', {
    value: obj,
  });
}, TypeError);

// Regression test with simple array
var arr = ['a'];
Object.freeze(arr);
arr[0] = 'b';
assertEquals(arr[0], 'a');

// Test regression Array.concat with double
var arr = ['a'];
Object.freeze(arr);
arr = arr.concat(0.5);
assertEquals(arr, ['a', 0.5]);
Object.freeze(arr);
arr = arr.concat([1.5, 'b']);
assertEquals(arr, ['a', 0.5, 1.5, 'b']);

// Regression test with change length
var arr = ['a', 'b'];
Object.freeze(arr);
assertEquals(arr.length, 2);
arr.length = 3;
assertEquals(arr.length, 2);
arr[2] = 'c';
assertEquals(arr[2], undefined);
arr.length = 1;
assertEquals(arr.length, 2);

// Start testing with holey array
// Test holey element array built-in functions with freeze.
function testHoleyFrozenArray1(obj) {
  assertTrue(Object.isSealed(obj));
  // Verify that the value can't be written
  obj1 = new Array(...obj);
  var length = obj.length;
  for (var i = 0; i < length-1; i++) {
    obj[i] = 'new';
    assertEquals(obj1[i], obj[i]);
  }
  // for symbol we cannot compare directly
  assertTrue(typeof obj[length-1] == 'symbol');

  // Verify that the length can't be written by builtins.
  assertTrue(Array.isArray(obj));
  assertThrows(function() { obj.pop(); }, TypeError);
  assertThrows(function() { obj.push(); }, TypeError);
  assertThrows(function() { obj.shift(); }, TypeError);
  assertThrows(function() { obj.unshift(); }, TypeError);
  assertThrows(function() { obj.copyWithin(0,0); }, TypeError);
  assertThrows(function() { obj.fill(0); }, TypeError);
  assertThrows(function() { obj.reverse(); }, TypeError);
  assertThrows(function() { obj.sort(); }, TypeError);
  assertThrows(function() { obj.splice(0); }, TypeError);
  assertThrows(function() { obj.splice(0, 0); }, TypeError);
  assertTrue(Object.isFrozen(obj));

  // Verify search, filter, iterator
  assertEquals(obj.lastIndexOf(1), 2);
  assertEquals(obj.indexOf('a'), 5);
  assertEquals(obj.indexOf(undefined), 0);
  assertFalse(obj.includes(Symbol("test")));
  assertTrue(obj.includes(undefined));
  assertFalse(obj.includes(NaN));
  assertTrue(obj.includes());
  assertEquals(obj.find(x => x==0), undefined);
  assertEquals(obj.findIndex(x => x=='a'), 5);
  assertTrue(obj.some(x => typeof x == 'symbol'));
  assertFalse(obj.every(x => x == -1));
  var filteredArray = obj.filter(e => typeof e == "symbol");
  assertEquals(filteredArray.length, 1);
  assertEquals(obj.map(x => x), obj);
  var countPositiveNumber = 0;
  obj.forEach(function(item, index) {
    if (item === 1) {
      countPositiveNumber++;
      assertEquals(index, 2);
    }
  });
  assertEquals(countPositiveNumber, 1);
  assertEquals(obj.length, obj.concat([]).length);
  var iterator = obj.values();
  assertEquals(iterator.next().value, undefined);
  assertEquals(iterator.next().value, null);
  var iterator = obj.keys();
  assertEquals(iterator.next().value, 0);
  assertEquals(iterator.next().value, 1);
  var iterator = obj.entries();
  assertEquals(iterator.next().value, [0, undefined]);
  assertEquals(iterator.next().value, [1, null]);
}

obj = [undefined, null, 1, , -1, 'a', Symbol("test")];
assertTrue(%HasHoleyElements(obj));
Object.freeze(obj);
testHoleyFrozenArray1(obj);

// Verify change from sealed to frozen
obj = [undefined, null, 1, , -1, 'a', Symbol("test")];
assertTrue(%HasHoleyElements(obj));
Object.seal(obj);
Object.freeze(obj);
assertTrue(Object.isSealed(obj));
testHoleyFrozenArray1(obj);

// Verify change from non-extensible to frozen
obj = [undefined, null, 1, ,-1, 'a', Symbol("test")];
assertTrue(%HasHoleyElements(obj));
Object.preventExtensions(obj);
Object.freeze(obj);
assertTrue(Object.isSealed(obj));
testHoleyFrozenArray1(obj);

// Verify flat, map, slice, flatMap, join, reduce, reduceRight for frozen packed array
function testHoleyFrozenArray2(arr) {
  assertTrue(Object.isFrozen(arr));
  assertTrue(Array.isArray(arr));
  assertEquals(arr.map(x => [x]), [, ['a'], ['b'], ['c']]);
  assertEquals(arr.flatMap(x => [x]), ["a", "b", "c"]);
  assertEquals(arr.flat(), ["a", "b", "c"]);
  assertEquals(arr.join('-'), "-a-b-c");
  const reducer = (accumulator, currentValue) => accumulator + currentValue;
  assertEquals(arr.reduce(reducer), "abc");
  assertEquals(arr.reduceRight(reducer), "cba");
  assertEquals(arr.slice(0, 1), [,]);
  assertEquals(arr.slice(1, 2), ["a"]);
}
var arr1 = [, 'a', 'b', 'c'];
assertTrue(%HasHoleyElements(arr1));
Object.freeze(arr1);
testHoleyFrozenArray2(arr1);

// Verify change from sealed to frozen
var arr2 = [, 'a', 'b', 'c'];
assertTrue(%HasHoleyElements(arr2));
Object.seal(arr2);
Object.freeze(arr2);
testHoleyFrozenArray2(arr2);

// Verify change from non-extensible to frozen
var arr2 = [, 'a', 'b', 'c'];
assertTrue(%HasHoleyElements(arr2));
Object.preventExtensions(arr2);
Object.freeze(arr2);
testHoleyFrozenArray2(arr2);

// Test regression with Object.defineProperty
var obj = ['a', , 'b'];
obj.propertyA = 42;
obj[0] = true;
Object.freeze(obj);
assertThrows(function() {
  Object.defineProperty(obj, 'propertyA', {
    value: obj,
  });
}, TypeError);
assertEquals(42, obj.propertyA);
assertThrows(function() {
  Object.defineProperty(obj, 'propertyA', {
    value: obj,
    writable: false,
  });
}, TypeError);
assertDoesNotThrow(function() {obj.propertyA = 2;});
assertEquals(obj.propertyA, 42);
assertThrows(function() {
  Object.defineProperty(obj, 'abc', {
    value: obj,
  });
}, TypeError);

// Regression test with simple holey array
var arr = [, 'a'];
Object.freeze(arr);
arr[1] = 'b';
assertEquals(arr[1], 'a');
arr[0] = 1;
assertEquals(arr[0], undefined);

// Test regression Array.concat with double
var arr = ['a', , 'b'];
Object.freeze(arr);
arr = arr.concat(0.5);
assertEquals(arr, ['a', ,'b', 0.5]);
Object.freeze(arr);
arr = arr.concat([1.5, 'c']);
assertEquals(arr, ['a', ,'b', 0.5, 1.5, 'c']);

// Regression test with change length
var arr = ['a', ,'b'];
Object.freeze(arr);
assertEquals(arr.length, 3);
arr.length = 4;
assertEquals(arr.length, 3);
arr[3] = 'c';
assertEquals(arr[2], 'b');
assertEquals(arr[3], undefined);
arr.length = 2;
assertEquals(arr.length, 3);

// Change length with holey entries at the end
var arr = ['a', ,];
Object.freeze(arr);
assertEquals(arr.length, 2);
arr.length = 0;
assertEquals(arr.length, 2);
arr.length = 3;
assertEquals(arr.length, 2);
arr.length = 0;
assertEquals(arr.length, 2);