v8/test/mjsunit/object-create.js

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// Test ES5 sections 15.2.3.5 Object.create.
// We do not support nonconfigurable properties on objects so that is not
// tested.  We do test getters, setters, writable, enumerable and value.

// Check that no exceptions are thrown.
Object.create(null);
Object.create(null, undefined);

// Check that the right exception is thrown.
try {
  Object.create(4);
  assertTrue(false);
} catch (e) {
  assertTrue(/Object or null/.test(e));
}

try {
  Object.create("foo");
  print(2);
  assertTrue(false);
} catch (e) {
  assertTrue(/Object or null/.test(e));
}

var ctr = 0;
var ctr2 = 0;
var ctr3 = 0;
var ctr4 = 0;
var ctr5 = 0;
var ctr6 = 1000;

var protoFoo = { foo: function() { ctr++; }};
var fooValue = { foo: { writable: true, value: function() { ctr2++; }}};
var fooGetter = { foo: { get: function() { return ctr3++; }}};
var fooSetter = { foo: { set: function() { return ctr4++; }}};
var fooAmbiguous = { foo: { get: function() { return ctr3++; },
                            value: 3 }};

function valueGet() { ctr5++; return 3 };
function getterGet() { ctr5++; return function() { return ctr6++; }; };

// Simple object with prototype, no properties added.
Object.create(protoFoo).foo();
assertEquals(1, ctr);

// Simple object with object with prototype, no properties added.
Object.create(Object.create(protoFoo)).foo();
assertEquals(2, ctr);

// Add a property foo that returns a function.
var v = Object.create(protoFoo, fooValue);
v.foo();
assertEquals(2, ctr);
assertEquals(1, ctr2);

// Ensure the property is writable.
v.foo = 42;
assertEquals(42, v.foo);
assertEquals(2, ctr);
assertEquals(1, ctr2);

// Ensure by default properties are not writable.
v = Object.create(null, { foo: {value: 103}});
assertEquals(103, v.foo);
v.foo = 42;
assertEquals(103, v.foo);

// Add a getter foo that returns a counter value.
assertEquals(0, Object.create(protoFoo, fooGetter).foo);
assertEquals(2, ctr);
assertEquals(1, ctr2);
assertEquals(1, ctr3);

// Add a setter foo that runs a function.
assertEquals(1, Object.create(protoFoo, fooSetter).foo = 1);
assertEquals(2, ctr);
assertEquals(1, ctr2);
assertEquals(1, ctr3);
assertEquals(1, ctr4);

// Make sure that trying to add both a value and a getter
// will result in an exception.
try {
  Object.create(protoFoo, fooAmbiguous);
  assertTrue(false);
} catch (e) {
  assertTrue(/Invalid property/.test(e));
}
assertEquals(2, ctr);
assertEquals(1, ctr2);
assertEquals(1, ctr3);
assertEquals(1, ctr4);

var ctr7 = 0;

var metaProps = {
  enumerable: { get: function() {
                       assertEquals(0, ctr7++);
                       return true;
                     }},
  configurable: { get: function() {
                         assertEquals(1, ctr7++);
                         return true;
                       }},
  value: { get: function() {
                  assertEquals(2, ctr7++);
                  return 4;
                }},
  writable: { get: function() {
                     assertEquals(3, ctr7++);
                     return true;
                   }},
  get: { get: function() {
                assertEquals(4, ctr7++);
                return function() { };
              }},
  set: { get: function() {
                assertEquals(5, ctr7++);
                return function() { };
              }}
};


// Instead of a plain props object, let's use getters to return its properties.
var magicValueProps = { foo: Object.create(null, { value: { get: valueGet }})};
var magicGetterProps = { foo: Object.create(null, { get: { get: getterGet }})};
var magicAmbiguousProps = { foo: Object.create(null, metaProps) };

assertEquals(3, Object.create(null, magicValueProps).foo);
assertEquals(1, ctr5);

assertEquals(1000, Object.create(null, magicGetterProps).foo);
assertEquals(2, ctr5);

// See if we do the steps in ToPropertyDescriptor in the right order.
// We shouldn't throw the exception for an ambiguous properties object
// before we got all the values out.
try {
  Object.create(null, magicAmbiguousProps);
  assertTrue(false);
} catch (e) {
  assertTrue(/Invalid property/.test(e));
  assertEquals(6, ctr7);
}

var magicWritableProps = {
  foo: Object.create(null, { value: { value: 4 },
                             writable: { get: function() {
                                                ctr6++;
                                                return false;
                                              }}})};

var fooNotWritable = Object.create(null, magicWritableProps)
assertEquals(1002, ctr6);
assertEquals(4, fooNotWritable.foo);
fooNotWritable.foo = 5;
assertEquals(4, fooNotWritable.foo);


// Test enumerable flag.

var fooNotEnumerable =
    Object.create({fizz: 14}, {foo: {value: 3, enumerable: false},
                               bar: {value: 4, enumerable: true},
                               baz: {value: 5}});
var sum = 0;
for (x in fooNotEnumerable) {
  assertTrue(x === 'bar' || x === 'fizz');
  sum += fooNotEnumerable[x];
}
assertEquals(18, sum);


try {
  Object.create(null, {foo: { get: 0 }});
  assertTrue(false);
} catch (e) {
  assertTrue(/Getter must be a function/.test(e));
}

try {
  Object.create(null, {foo: { set: 0 }});
  assertTrue(false);
} catch (e) {
  assertTrue(/Setter must be a function/.test(e));
}

try {
  Object.create(null, {foo: { set: 0, get: 0 }});
  assertTrue(false);
} catch (e) {
  assertTrue(/Getter must be a function/.test(e));
}


// Ensure that only enumerable own properties on the descriptor are used.
var tricky = Object.create(
  { foo: { value: 1, enumerable: true }},
  { bar: { value: { value: 2, enumerable: true }, enumerable: false },
    baz: { value: { value: 4, enumerable: false }, enumerable: true },
    fizz: { value: { value: 8, enumerable: false }, enumerable: false },
    buzz: { value: { value: 16, enumerable: true }, enumerable: true }});

assertEquals(1, tricky.foo.value);
assertEquals(2, tricky.bar.value);
assertEquals(4, tricky.baz.value);
assertEquals(8, tricky.fizz.value);
assertEquals(16, tricky.buzz.value);

var sonOfTricky = Object.create(null, tricky);

assertFalse("foo" in sonOfTricky);
assertFalse("bar" in sonOfTricky);
assertTrue("baz" in sonOfTricky);
assertFalse("fizz" in sonOfTricky);
assertTrue("buzz" in sonOfTricky);

var sum = 0;
for (x in sonOfTricky) {
  assertTrue(x === 'buzz');
  sum += sonOfTricky[x];
}
assertEquals(16, sum);