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JavaScript Concepts: Simply the Best IF you often watch the HBO movies, then the title of this JavaScript post will be familiar to you: "Simply the Best". Yes, that's right, I want to borrow this slogan from HBO to describe the content of this post: it will provide you the very basic JavaScript concepts, and you will be able to access, understand the web programming JavaScript language easily and quickly.

This JavaScript article tutorial shows you the full-detailed practices, combined with live JavaScript example codes to try. At present, this JavaScript article tutorial us 5 parts and I'll update if there's new chapter, meanwhile, you can go through:
- Part 1: JavaScript Classes
- Part 2: JavaScript Inheritance
- Part 3: JavaScript and JSON
- Part 4: The Prototype Property
- Part 5: JavaScript Closures

Read more other JavaScript article tutorials on jsB@nk:
- JavaScript Function Declarations & JavaScript Function Expressions - Basic Concepts
- JavaScript Prototype: Some Basic Concepts
- 5 Chief JavaScript Inheritance Concepts
- Simple Concepts about Types and Objects in JavaScript OOP
- Top 10 Best JavaScript eBooks that Beginners should Learn


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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);

JavaScript by day


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