26/05/2011
3
Si vous avez souvent regarder les films de HBO , puis le titre de ce post JavaScript vous ?tre familier : Oui , c'est vrai , je veux emprunter ce slogan de HBO pour d?crire le contenu de ce post : il vous fournira les concepts de base JavaScript , et vous serez en mesure d' acc?der , de comprendre la programmation web langage JavaScript facilement et rapidement
Exemple, les codes JavaScript pour essayer ? l'heure actuelle , cet article JavaScript tutorial nous 5 pi?ces et je mettrai ? jour s'il ya nouveau chapitre , en attendant , vous pouvez passer par :
? D?clarations de fonctions JavaScript et des expressions de fonction JavaScript - Concepts de base
? JavaScript Prototype : Quelques concepts de base
? 5 Chef Concepts H?ritage JavaScript
? Concepts simples sur les types et les objets en JavaScript POO
? Top 10 Meilleurs livres JavaScript que les d?butants devraient apprendre
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While the Javascript language offers many of the constructs required for object-oriented programming, they remain largely unused. Today we�ll take a look at how to start with object-oriented programing in Javascript. by defining a class in Javascript. We�ll use the simple HTML file to call our script file,
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html> <head> <title>Hello Javascript!</title> <script type="text/javascript" src="MyScript.js"></script> </head> <body> Hello Javascript! </body> </html>
Now let�s create a class definition (in MyScript.js). Note that there is no �class� keyword in Javascript, the class definition is just a function definition,
function MyClass() { // Public field this.aPublicField = "This is a public field of the type MyClass"; // Private field var aPrivateField = "This is a private field of the type MyClass"; // Public method this.aPublicMethod = function() { // Use the private method if (aPrivateMethod()) { return this.aPublicField; } else { return aPrivateField; } } // Private method function aPrivateMethod() { return true; } // Oops! We can expose the private field this.exposePrivateField = aPrivateField; // and the private method this.exposePrivateMethod = aPrivateMethod; } // Create an instance of MyClass using the �new� keyword var myclass = new MyClass(); // Get the public field alert(myclass.aPublicField); // Call the public method alert(myclass.aPublicMethod()); // Call the private field � can�t get to them directly alert(myclass.exposePrivateField); alert(myclass.exposePrivateMethod());
So it�s pretty simple to create a class in Javascript. We can also create a runtime field for the class,
// Create an instance of MyClass var myclass = new MyClass(); // Create a field at runtime myclass.aRuntimeField = "This is a runtime field of the type MyClass"; // View the field value alert(myclass.aRuntimeField);
Part 2: Javascript Inheritance
Now that we created a base Javascript class in the first post, let�s inherit from it to get a derived class.
// Define the derived function (remember there is no 'class' keyword in Javascript) function MyDerivedClass() { } // Derive from MyClass, equivalent to �> public class MyDerivedClass : MyClass MyDerivedClass.prototype = new MyClass(); // Create an instance of the derived class var myderivedClass = new MyDerivedClass(); // Get the public field alert(myderivedClass.aPublicField); // Call the public method alert(myderivedClass.aPublicMethod());
Woah! That was simple! Notice that MyClass�s private methods and the runtime field (aRuntimeField) we gave to MyClass in the last post is not available to MyDerivedClass.
Let�s override the base classe�s public fields and methods and see what happens,
// Define the derived function (remember there is no 'class' keyword in Javascript function MyDerivedClass() { // Override the base's public field this.aPublicField = "This is a public field of the type MyDerivedClass"; // Override the base's public method this.aPublicMethod = function() { return this.aPublicField; } } // Derive from MyClass, equivalent to �> public class MyDerivedClass : MyClass MyDerivedClass.prototype = new MyClass(); // Create an instance of the derived class var myderivedClass = new MyDerivedClass(); // Get the public field alert(myderivedClass.aPublicField); // Call the public method alert(myderivedClass.aPublicMethod());
You�ll see that the base classes public fields and methods have been overridden in the derived class.
We can obviously derive again,
// Derive from MyDerivedClass function MyDerivedDerivedClass() { // Override the base's public field this.aPublicField = "This is a public field of the type MyDerivedDerivedClass"; // Override the base's public method this.aPublicMethod = function() { return this.aPublicField; } } // Derive from MyDerivedClass, equivalent to �> public class MyDerivedDerivedClass : MyDerivedClass MyDerivedDerivedClass.prototype = new MyDerivedClass(); // Create an instance of the derived class var myderivedderivedClass = new MyDerivedDerivedClass(); // Call the public method alert(myderivedderivedClass.aPublicField);
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Soumya Chattopadhyay [more]
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26/05/2011
Si vous avez souvent regarder les films de HBO , puis le titre de ce post JavaScript vous ?tre familier : Oui , c'est vr...Concepts JavaScript : Simply the Best - Concepts JavaScript : Simply the Best
