Object : undefined

Object is the base in the prototype chain.

JavaScript **Object**s can have any number values stored as properties

(specified by %%/String|**String**%% names or %%/Symbol|**Symbol**%%s).

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2

----

Object() : Object

Same as %%#new_Object_|**new Object()**%%.

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.1.1

----

Object(value : Object) : Object

Same as %%#new_Object_Object|**new Object(value)**%%.

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.1.1

----

new Object() : Object

Creates an empty object.

Can also be constructed as **{}**.

<example>

// The following are all equivalent

var x = {};

var y = Object();

var z = new Object();

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.2.1

----

new Object(value : Object) : Object

If **value** is a primitive type, creates a box for **value**. Otherwise,

returns **value**.

<example>

var x = true;

console.log(typeof x + ' / ' + typeof Object(x));

console.log(x === Object(x));

var y = {};

console.log(typeof y + ' / ' + typeof Object(y));

console.log(y === Object(y));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.2.1

----

instance[propertyName : String] : Object

Returns the value stored in this at the specified **propertyName**.

This is the same as the **.** style access but also allows the

property name to be specified at runtime using a String of being hardcoded and allows

access to properties that are invalid identifiers (such as including spaces or

starting with a number).

<example>

var x = { foo: 'bar'};

// The following are equivalent

console.log(x.foo);

console.log(x['foo']);

// Use [] indexing when the name is not known ahead of time

var propertyName = 'f' + 'oo';

console.log(x[propertyName]);

</example>

----

instance[symbol : Symbol] : Object

Returns the value stored in this at the specified **symbol**.

<example>

var x = { foo: 'bar'};

</example>

Version:

ECMAScript 2015

----

getPrototypeOf(obj : Object) : Object

Returns the prototype of **obj**.

<example>

console.log(Object.getPrototypeOf([]) === Array.prototype);

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.2

----

getOwnPropertyDescriptor(obj : Object, propertyName : String) : PropertyDescriptor

Returns a **PropertyDescriptor** that describes the **propertyName** property on **obj**.

<example>

var x = { foo: 1,

get bar() {

return 'a';

} };

Object.defineProperty(x, 'baz', { value: 2,

writable: true,

enumerable: false,

configurable: true } );

console.dir(Object.getOwnPropertyDescriptor(x, 'foo'));

console.dir(Object.getOwnPropertyDescriptor(x, 'bar'));

console.dir(Object.getOwnPropertyDescriptor(x, 'baz'));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.3

----

getOwnPropertyNames(obj : Object) : Array<String>

Returns an **Array** of the names of all properties set on **obj** including

those that are not enumerable.

See also %%#keys|**keys()**%%.

<example>

var x = { foo: 1 };

Object.defineProperty(x, 'bar', { value: 2,

writable: true,

enumerable: false,

configurable: true } );

console.log(Object.keys(x));

console.log(Object.getOwnPropertyNames(x));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.4

----

getOwnPropertySymbols(obj : Object) : Array<Symbol>

Returns an **Array** of the symbols of properties set on **obj** including

those that are not enumerable.

<example>

var myObject = { foo: 'bar' };

var mySymbol = Symbol('MySymbol');

myObject[mySymbol] = 'baz';

for (var symbol of Object.getOwnPropertySymbols(myObject)) {

console.log('myObject[' + symbol.toString() + '] = ' + myObject[symbol]);

}

</example>

Version:

ECMAScript 2015

Spec:

http://www.ecma-international.org/ecma-262/6.0/#sec-object.getownpropertysymbols

----

create(prototype : Object, [propertyDescriptors : Object]) : Object

Returns a new **Object** with prototype equal to **prototype**. Pass

**null** for **prototype** to create an object with no prototype.

Calls

%%#defineProperties|**defineProperties(obj, propertyDescriptors)**%%

with the new object if **propertyDescriptors** is specified.

<example>

var x = Object.create({}, { foo: { value: 1,

writable: true,

enumerable: true,

configurable: true },

bar: { value: 2,

writable: true,

enumerable: false,

configurable: true }});

console.log(x.foo);

console.log(x.bar);

console.log(Object.keys(x));

console.log(Object.getOwnPropertyNames(x));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.5

----

defineProperty(obj : Object, propertyName : String, propertyDescriptor : PropertyDescriptor) : Object

Defines a new property with name equal to **propertyName** on **obj** with the

supplied descriptor. Returns **obj**.

<example>

var x = { foo: 1 };

Object.defineProperty(x, 'bar', { value: 2,

writable: true,

enumerable: false,

configurable: true } );

console.log(x.foo);

console.log(x.bar);

console.log(Object.keys(x));

console.log(Object.getOwnPropertyNames(x));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.6

----

defineProperties(obj : Object, propertyDescriptors : Object) : Object

For each property on **propertyDescriptors**, defines a new property on

**obj** with the same name and supplied %%/PropertyDescriptor|**PropertyDescriptor**%%.

Returns **obj**.

<example>

var x = {};

Object.defineProperties(x, { foo: { value: 1,

writable: true,

enumerable: true,

configurable: true },

bar: { value: 2,

writable: true,

enumerable: false,

configurable: true }});

console.log(x.foo);

console.log(x.bar);

console.log(Object.keys(x));

console.log(Object.getOwnPropertyNames(x));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.7

----

seal(obj : Object) : Object

Same as %%#preventExtensions|**preventExtensions**%% except it also

sets each property as not

%%/PropertyDescriptor#configurable|**configurable**%%. Returns **obj**.

<example>

var x = { foo: 1 };

Object.seal(x);

x.foo = 3;

console.log(x.foo);

x.bar = 1;

console.log(x.bar);

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.8

----

freeze(obj : Object) : Object

For each property on **obj**, sets its

%%/PropertyDescriptor#configurable|**PropertyDescriptor.configurable**%%

property to **false** and

%%/PropertyDescriptor#writable|**PropertyDescriptor.writable**%%

property to **false**. Also calls

%%#preventExtensions|**preventExtensions**%% on **obj**. Returns **obj**.

<example>

var x = { foo: 1 };

Object.freeze(x);

x.foo = 3;

console.log(x.foo);

x.bar = 1;

console.log(x.bar);

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.9

----

preventExtensions(obj : Object) : Object

Prevents new properties from being added to **obj**. Unlike %%#freeze|**freeze**%%, existing

properties can be modified. Returns **obj**.

<example>

var x = { foo: 1 };

Object.preventExtensions(x);

x.foo = 3;

console.log(x.foo);

x.bar = 1;

console.log(x.bar);

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.10

----

isSealed(obj : Object) : Boolean

Returns **true** if %%#seal|**seal**%% was called on **obj**. A sealed object cannot have

new properties added to it but the value of existing properties can be changed.

<example>

var x = { foo: 1 };

Object.seal(x);

console.log(Object.isSealed(x));

console.log(Object.isExtensible(x));

console.log(Object.isFrozen(x));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.11

----

isFrozen(obj : Object) : Boolean

Returns **true** if %%#freeze|**freeze**%% was called on **obj**. A frozen object cannot have

new properties added and existing properties cannot be modified.

<example>

var x = { foo: 1 };

Object.freeze(x);

console.log(Object.isSealed(x));

console.log(Object.isExtensible(x));

console.log(Object.isFrozen(x));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.12

----

isExtensible(obj : Object) : Boolean

Returns **false** if %%#preventExtensions|**preventExtensions**%% was called on **obj**. A

non-extensible object cannot have new properties added to it.

<example>

var x = { foo: 1 };

console.log(Object.isExtensible(x));

Object.preventExtensions(x);

console.log(Object.isExtensible(x));

console.log(Object.isSealed(x));

console.log(Object.isFrozen(x));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.13

----

keys(obj : Object) : Array<String>

Returns an **Array** containing the enumerable properties on **obj**.

See also %%#getOwnPropertyNames|**getOwnPropertyNames()**%%.

<example>

var x = { foo: 1, bar: 2 };

console.log(Object.keys(x));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.14

----

prototype.constructor : Function

The **Function** that constructed **this**.

<example>

console.log({}.constructor === Object);

console.log([].constructor === Array);

console.log('foo'.constructor === String);

</example>

----

prototype.toString() : String

Returns a string representation of **this**. This method is called

each time the object is used in a place a string is expected. Define your own

**toString** to give a better string representation to your objects.

<example>

var pt = { x: 1, y: 2 };

console.log(pt);

pt.toString = function() {

return '(' + this.x + ', ' + this.y + ')';

};

console.log(pt);

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.4.2

----

prototype.toLocaleString() : String

Returns a locale specific (if possible) string representation of **this**.

<example>

var x = 1.234;

console.log(x.toString());

console.log(x.toLocaleString());

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.4.3

----

prototype.valueOf() : Object

For boxed primitive types, returns the unboxed value.

<example>

var x = Object(1);

console.log(x === 1);

console.log(x.valueOf() === 1);

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.4.4

----

prototype.hasOwnProperty(propertyName : String) : Boolean

Returns **true** if **this** has a property named **propertyName** stored on it.

This method can be used to see if a property is set on the object, even

if the value is set to **undefined**.

Properties stored in the prototype chain do not count.

<example>

var x = { foo: 1 };

console.log(x.hasOwnProperty('foo'));

console.log(x.hasOwnProperty('bar'));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.4.5

----

prototype.isPrototypeOf(obj : Object) : Boolean

Returns **true** if **this** is in the prototype chain of **obj**.

<example>

// Array instances are Objects

console.log(Object.prototype.isPrototypeOf(Array.prototype));

// Array instances are not Functions

console.log(Function.prototype.isPrototypeOf(Array.prototype));

// Array constructor is a Function

console.log(Function.prototype.isPrototypeOf(Array));

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.4.6

----

prototype.propertyIsEnumerable(propertyName : String) : Boolean

Returns **true** if the property named **propertyName** on **this** is

enumerable and should be returned during a **for (x in y)** loop.

<example>

var x = { foo: 1 };

Object.defineProperty(x, 'bar', { value: 2,

writable: true,

enumerable: false,

configurable: true } );

console.log(x.propertyIsEnumerable('foo'));

console.log(x.propertyIsEnumerable('bar'));

for (var propertyName in x) {

console.log(propertyName + ' is ' + x[propertyName]);

}

</example>

Spec:

http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.4.7