The JavaScript Object object is for creating custom objects that you may assign custom properties and methods to. Property values can be assorted data types such as String, Number, Boolean, Object, Array, etc…

Create a new empty object instance

var player1 = new Object(); // or
var player1 = { };

Assign Properties

// Using dot notation
player1.name = "Gandalf"; player1.hitpoints = 100; player1.spells = ["Lightning","Fire Ball","Ice Storm"]; // Using square brackets
player1["name"] = "Gandalf"; player1["hitpoints"] = 100; player1["spells"] = ["Lightning","Fire Ball","Ice Storm"]; // Using object literal notation(object initializer)
player1 = { name: "Gandalf", hitpoints: 100, spells: ["Lightning","Fire Ball","Ice Storm"] };

Reading Specific Property Values

alert( player1.name ); alert( player1.spells ); alert( player1.spells[1] );

List All Properties (loop over object properties)

for( var prop in player1 ){ document.write( prop + " - " + player1[prop] + "<br>" ); }

Assigning Methods

// Assign a custom method to the object
player1.takeDamage = function(amount){ this.hitpoints -= amount; }; // Run that method now
player1.takeDamage(20); // Show some results
alert( player1.hitpoints );

Constructor Function

In order to create object oriented code(like class programming in other languages), we use constructor functions for establishing object instances. This also provides a way to prevent data collisions or value conflicts in dynamic mechanisms that many instances might use simultaneously.

// Create the PlayerClass constructor
function PlayerClass(){ // Properties
this.name; this.hitpoints = 100; // Methods
this.takeDamage = function(amount){ this.hitpoints -= amount; }; } // Create new instances of the PlayerClass
var p1 = new PlayerClass(); var p2 = new PlayerClass(); // Adjust property values
p1.name = "Gandalf"; p2.name = "Mysterio"; // Inflict damage to each player
p1.takeDamage(5); p2.takeDamage(10); // Show some results
alert(p1.name+" | "+p1.hitpoints); alert(p2.name+" | "+p2.hitpoints);


prototype Property

The prototype property allows authors to add properties and methods to objects(or alter their default properties). There may be occasions when you must specialize or extend an object in a script. You can also use the prototype property on built-in objects that JavaScript offers like Array, Number, String, etc…, not only on custom objects.

// Add a heal method to the PlayerClass using the prototype property
PlayerClass.prototype.heal = function(player, amount){ player.hitpoints += amount; }; // Make player2 heal player1
p2.heal(p1, 5); alert(p1.name+" | "+p1.hitpoints);



Inheritance is making an object inherit all of the properties and methods of another object, to become a specialized version of the other object. We use the prototype property to make a subclass inherit the characteristics of a parent class. This results in a specialized subclass that can retain its own properties and methods, as well as inherit all of the properties and methods of the parent class.

// Establish a parent class
function Parentclass(){ this.parent_property1 = "Hola"; this.parentmethod1 = function(arg1){ return arg1+" Parent method 1 return data ..."; } } // Establish a child class
function Childclass(){ this.child_property1 = "Adios"; this.childmethod1 = function(arg1){ return arg1+" Child method 1 return data ..."; } } // Make the Childclass inherit all of the Parent class characteristics
Childclass.prototype = new Parentclass(); // Create a new instance of Childclass
var instance1 = new Childclass(); // Check to see if instance1 is an instance of both objects
alert( instance1 instanceof Parentclass ); alert( instance1 instanceof Childclass ); // Access the instance methods and properties
alert( instance1.parentmethod1("RESULT: ") ); alert( instance1.childmethod1("RESULT: ") ); alert( instance1.parent_property1 ); alert( instance1.child_property1 ); // Override parentmethod1 in the Childclass
Childclass.prototype.parentmethod1 = function(arg1){ return arg1+" I have overridden Parent method 1"; } alert( instance1.parentmethod1("RESULT: ") );


JSON objects are instances of Object objects

var user = { "name": "Henry", "age": 27, "country": "China" }; alert( user instanceof Object ); alert( user.constructor ); alert( user.name );



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