JavaScript Tutorials - Herong's Tutorial Examples - 2.33, by Herong Yang
Adding Properties and Methods to Objects
This section provides a quick description of adding properties and methods to objects only. A tutorial example is provided on adding 1 extra property and 1 extra method to 1 object only.
After an object has been created from the constructor function, additional properties and methods can be added to this object only, using these formats:
object_name.property_name = initial_value; object_name.method_name = function_name;
Here is tutorial example that creates two objects from "Book()", and adds 1 extra property and 1 extra method to object "myBook" only:
<html> <!-- Prototype_Add_Property_and_Method.html Copyright (c) 2008 HerongYang.com. All Rights Reserved. --> <head> <title>Adding Additional Properties and Methods to Objects</title> </head> <body> <pre> <script type="text/javascript"> // Defining the constructor function for a new object type function Book(title, author) { this.title = title; this.author = author; } // Defining a function to be used as a method function getDescription() { return "\""+this.title+"\" by "+this.author; } // Creating an object of "Book" var myBook = new Book("JavaScript Tutorials", "Herong Yang"); var ckBook = new Book("JavaScript Cookbook", "Yosef Cohen"); // Adding additional property and method to one object myBook.price = 99.99; myBook.getDesc = getDescription; // Showing object properties and methods showObject(myBook, "myBook"); showObject(ckBook, "ckBook"); function showObject(object, name) { document.writeln("\nShowing object \""+name+"\""); document.writeln(" Own Properties and Methods:"); for (var item in object) { document.writeln(" "+item+": "+object[item]); } } </script> </pre> </body> </html>
The output of the tutorial example shows that properties defined in the constructor function are added to both objects. But properties and methods added to object "myBook" are for "myBook" only.
Showing object "myBook" Own Properties and Methods: title: JavaScript Tutorials author: Herong Yang price: 99.99 getDesc: function getDescription() { return "\"" + this.title + "\" by " + this.author; } Showing object "ckBook" Own Properties and Methods: title: JavaScript Cookbook author: Yosef Cohen
Table of Contents
ECMAScript Language Specification and JavaScript Dialects
Data Types, Variables and Expressions
Creating, Accessing, and Manipulating Arrays
Defining and Calling Functions
Web Browser Supporting JavaScript
Server-Side and Client-Side Web Scripting
►Defining Your Own Object Types
Prototype-Dased Object-Oriented Programming Style
Prototype-Based Programming Features in JavaScript
Defining Object Constructor Functions
►Adding Properties and Methods to Objects
"for ... in" and "for each ... in" Statements
"prototype" Property of the Constructor Function Object
"instanceof" Operator - Determining Object Type
"typeof" Operator and Data Types
Inheritance of Properties and Methods through the Prototype Object Chain
'jrunscript' - JavaScript Shell Command from JDK
Using Functions as "Function" Objects
Introduction to Built-in Object Types
W3C's Document Object Model (DOM) Specifications