JavaScript Tutorial - Abstract classes in JavaScript

Link for all dot net and sql server video tutorial playlists http://www.youtube.com/user/kudvenkat/playlists Link for slides, code samples and text version of the video http://csharp-video-tutorials.blogspot.com/2015/02/abstract-classes-in-javascript.html Healthy diet is very important both for the body and mind. If you like Aarvi Kitchen recipes, please support by sharing, subscribing and liking our YouTube channel. Hope you can help. https://www.youtube.com/channel/UC7sEwIXM_YfAMyonQCrGfWA/?sub_confirmation=1 In this video we will discuss, how to implement abstract classes concept in JavaScript. Object oriented programming languages like C# and Java, support abstract classes. Abstract classes are incomplete. So, trying to create an instance of an abstract class raises a compiler error. Abstract classes can only be used as base classes. Let us first look at a simple C# example. 1. Open visual studio and create a new empty asp.net web application project. 2. Add a webform to the project. Name it WebForm1.aspx. Copy and past the following code in the code-behind file. using System; namespace Demo { public partial class WebForm1 : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { // Error: Cannot create an instance of an abstract class // Shape s = new Shape(); Circle circle = new Circle(); circle.shapeName = "Circle"; Response.Write(circle.draw() + "[br/][br/]"); Response.Write(circle is Shape + "[br/]"); // Returns true Response.Write(circle is Circle + "[br/]"); // Returns true } } public abstract class Shape { public string shapeName = "None"; public string draw() { return "Drawing " + this.shapeName; } } public class Circle : Shape { // Code specific to Circl class } } Since JavaScript is also an object oriented programming language, it also supports the concept of abstract classes. Here is an example. Add a new HTML page to the project. Name it HTMLPage1.htm. Copy and paste the following code in HTMLPage1.htm. [script type="text/javascript"] // Create a Shape object which is abstract var Shape = function () { this.shapeName = "None"; throw new Error("Cannot create an instance of abstract class"); } // Error : Cannot create an instance of abstract class // var shape = new Shape(); // Add draw function to the Shape prototype // Objects derived from Shape should be able to call draw() method Shape.prototype.draw = function () { return "Drwaing " + this.shapeName; } // Create a Circle object var Circle = function (shapeName) { this.shapeName = shapeName; } // Make shape the parent for Circle // Object.create() allows to create an object without using constructor Circle.prototype = Object.create(Shape.prototype); var circle = new Circle("Circle"); // Since Circle inherits from abstract Shape object, it can call draw() method document.write(circle.draw()); alert(circle instanceof Circle); // Returns true alert(circle instanceof Shape); // Returns true [/script]