Microsoft AJAX Library - JavaScript Classes

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Create New Class Instance

JavaScript Class Diagrams

Create New Class Instance

Page 2 of 3

Create New Class Instance

Once your new class is created, you use it just as you'd use a C# class. For example, this is how you'd create a new class instance, and call its DisplayGreeting() method:

Sample Code

// create class instance
var myHello = new HelloWorld()
// call method
myHello.DisplayGreeting()

A possible implementation of the HelloWorld class is the following:

Sample Code

// "Hello, World" class
function HelloWorld(hour)
{
// class "constructor" initializes this.hour field
if (hour)
{
// if the hour parameter has a value, store it as a class field
this.hour = hour
}
else
{
// if the hour parameter doesn't exist, save the current hour
var date = new Date()
this.hour = date.getHours()
}
// display greeting
this.DisplayGreeting = function()
{
if (this.hour >= 22 this.hour <= 5)
document.write("Goodnight, world!")
else
document.write("Hello, world!")
}
}

This code can be tested online at http://www.cristiandarie.ro/asp-ajax/ JavaScriptClass.html. The HelloWorld class is formed of the constructor code that initializes the hour field (this.hour), and of the DisplayGreeting() method—this.DisplayGreeting(). Fans of the ternary operator can rewrite the constructor using this shorter form, which also makes use of the object detection feature that was discussed in Chapter 2:

Sample Code

// define and initialize this.hour
this.hour = (hour) ? hour : (new Date()).getHours()

NOTE: The ternary operator is supported both by C# and JavaScript. It has the form (condition ? valueA : valueB). If the condition is true, the expression returns valueA, otherwise it returns valueB. In the shown example, object detection is used to test if a value was supplied for the hour parameter. If it was not, the current hour is used instead.

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Microsoft AJAX Library - JavaScript Classes

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Create New Class Instance

Create New Class Instance

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