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    Object.prototype

    Summary

    The Object.prototype property represents the Object prototype object.

    Property attributes of Object.prototype
    Writable no
    Enumerable no
    Configurable no

    Description

    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() 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.

    Properties

    Object.prototype.constructor
    Specifies the function that creates an object's prototype.
    Object.prototype.__proto__
    Points to the object which was used as prototype when the object was instantiated.
    Object.prototype.__noSuchMethod__
    Allows a function to be defined that will be executed when an undefined object member is called as a method.
    Object.prototype.__count__
    Used to return the number of enumerable properties directly on a user-defined object, but has been removed.
    Object.prototype.__parent__
    Used to point to an object's context, but has been removed.

    Methods

    Object.prototype.__defineGetter__()
    Associates a function with a property that, when accessed, executes that function and returns its return value.
    Object.prototype.__defineSetter__()
    Associates a function with a property that, when set, executes that function which modifies the property.
    Object.prototype.__lookupGetter__()
    Returns the function associated with the specified property by the __defineGetter__ method.
    Object.prototype.__lookupSetter__()
    Returns the function associated with the specified property by the __defineSetter__ 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()
    Returns a boolean indication whether the specified object is in the prototype chain of the object this method is called upon.
    Object.prototype.propertyIsEnumerable()
    Returns a boolean indicating if the internal ECMAScript DontEnum attribute is set.
    Object.prototype.toSource()
    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()
    Calls toString().
    Object.prototype.toString()
    Returns a string representation of the object.
    Object.prototype.unwatch()
    Removes a watchpoint from a property of the object.
    Object.prototype.valueOf()
    Returns the primitive value of the specified object.
    Object.prototype.watch()
    Adds a watchpoint to a property of the object.
    Object.prototype.eval()
    Used to evaluate a string of JavaScript code in the context of the specified object, but has been removed.

    Examples

    Since Javascript doesn't exactly have sub-class objects, prototype is a useful workaround to make a “base class” object of certain functions that act as objects. For example:

    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();
    joe.greet();
    rg.greet();
    mike.greet();
    mime.greet();
    

    This will output:

    Hi, I am Bob, the Builder
    Hi, I am Joe
    Hi, I am Red Green, the Handyman
    Hi, I am Mike
    

    Specifications

    Specification Status Comment
    ECMAScript 1st Edition. Implemented in JavaScript 1.0. Standard Initial definition.
    ECMAScript 5.1 (ECMA-262)
    The definition of 'Object.prototype' in that specification.
    Standard  
    ECMAScript 2015 (6th Edition, ECMA-262)
    The definition of 'Object.prototype' in that specification.
    Standard  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

    See also

    Document Tags and Contributors

    Last updated by: fscholz,