Training Guide: Programming in HTML5 with JavaScript and CSS3 Ebook

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Chapter 9 Asynchronous operations

CHAPTER 9 Asynchronous operations

H

ave you ever run an application and had the screen freeze when you clicked a button?

You waited until its operation completed, and then the application started working

again. Have you seen this behavior on webpages? You know that the problem is due to

long-running operations, but shouldn’t there be a better way to write this code?

The answer to these questions is to implement long-running operations as asynchronous

operations because these operations are currently synchronous operations. Synchronous

code has one sequential execution path, and when the long-running code is executing,

nothing else can be accomplished. What’s needed is another execution path so that the

long-running code can execute on one execution path while the user interface is responsive

on another execution path; this is what asynchronous operations do.

This chapter explores asynchronous operations, using jQuery and web workers.

Lessons in this chapter:

■■Lesson 1: Asynchronous operations using jQuery and WinJS 393

■■Lesson 2: Working with web workers 404

Before you begin

To complete this book, you must have some understanding of web development. This

chapter requires the hardware and software listed in the “System requirements” section in

the book’s Introduction.

Lesson 1: Asynchronous operations using jQuery and WinJS

An asynchronous operation is executed on a thread that is different from the main thread,

a thread being a separate execution path. The previous chapter provided a brief introduc-

tion to asynchronous programming when executing AJAX calls to the server. In addition to

jQuery’s support for using AJAX calls, you might want to perform local asynchronous calls

for operations that are time consuming. For example, if you are performing animations by

using jQuery, you’ll find that jQuery animations are performed asynchronously.

Key

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