Object.prototype

All objects in JavaScript are descended from Object; all objects inherit methods and properties from Object.prototype, although they may be overridden (except an Object with a null prototype, i.e. Object.create(null)). For example, other constructors' prototypes override the constructor property and provide their own toString() (en-US) methods. Changes to the Object prototype object are propagated to all objects unless the properties and methods subject to those changes are overridden further along the prototype chain.

Object.prototype.constructor (en-US)

Specifies the function that creates an object's prototype.

Object.prototype.__proto__ (en-US) Non-Standard

Points to the object which was used as prototype when the object was instantiated.

Object.prototype.__noSuchMethod__ Non-Standard

Allows a function to be defined that will be executed when an undefined object member is called as a method.

Object.prototype.__count__ Deprecated

Used to return the number of enumerable properties directly on a user-defined object, but has been removed.

Object.prototype.__parent__ Deprecated

Used to point to an object's context, but has been removed.

Object.prototype.__defineGetter__() (en-US) Non-Standard Deprecated

Associates a function with a property that, when accessed, executes that function and returns its return value.

Object.prototype.__defineSetter__() (en-US) Non-Standard Deprecated

Associates a function with a property that, when set, executes that function which modifies the property.

Object.prototype.__lookupGetter__() (en-US) Non-Standard Deprecated

Returns the function associated with the specified property by the __defineGetter__ (en-US) method.

Object.prototype.__lookupSetter__() (en-US) Non-Standard Deprecated

Returns the function associated with the specified property by the __defineSetter__ (en-US) method.

Object.prototype.hasOwnProperty()

Returns a boolean indicating whether an object contains the specified property as a direct property of that object and not inherited through the prototype chain.

Object.prototype.isPrototypeOf() (en-US)

Returns a boolean indication whether the specified object is in the prototype chain of the object this method is called upon.

Object.prototype.propertyIsEnumerable() (en-US)

Returns a boolean indicating if the internal ECMAScript DontEnum attribute is set.

Object.prototype.toSource() (en-US) Non-Standard

Returns string containing the source of an object literal representing the object that this method is called upon; you can use this value to create a new object.

Object.prototype.toLocaleString() (en-US)

Calls toString() (en-US).

Object.prototype.toString() (en-US)

Returns a string representation of the object.

Object.prototype.unwatch() Non-Standard

Removes a watchpoint from a property of the object.

Object.prototype.valueOf() (en-US)

Returns the primitive value of the specified object.

Object.prototype.watch() Non-Standard

Adds a watchpoint to a property of the object.

Object.prototype.eval() Deprecated

Used to evaluate a string of JavaScript code in the context of the specified object, but has been removed.

因為 JavaScript 並沒有子類別的物件，所以原型是個很有用的解決辦法, 使某些函數作為物件的基本類別物件。例如：

var Person = function() {
  this.canTalk = true;
};

Person.prototype.greet = function() {
  if (this.canTalk) {
    console.log('Hi, I am ' + this.name);
  }
};

var Employee = function(name, title) {
  Person.call(this);
  this.name = name;
  this.title = title;
};

Employee.prototype = Object.create(Person.prototype);
Employee.prototype.constructor = Employee;

Employee.prototype.greet = function() {
  if (this.canTalk) {
    console.log('Hi, I am ' + this.name + ', the ' + this.title);
  }
};

var Customer = function(name) {
  Person.call(this);
  this.name = name;
};

Customer.prototype = Object.create(Person.prototype);
Customer.prototype.constructor = Customer;

var Mime = function(name) {
  Person.call(this);
  this.name = name;
  this.canTalk = false;
};

Mime.prototype = Object.create(Person.prototype);
Mime.prototype.constructor = Mime;

var bob = new Employee('Bob', 'Builder');
var joe = new Customer('Joe');
var rg = new Employee('Red Green', 'Handyman');
var mike = new Customer('Mike');
var mime = new Mime('Mime');

bob.greet();
// Hi, I am Bob, the Builder

joe.greet();
// Hi, I am Joe

rg.greet();
// Hi, I am Red Green, the Handyman

mike.greet();
// Hi, I am Mike

mime.greet();

• Introduction to Object-Oriented JavaScript