Pro JavaScript for Web Apps pdf - EBook Free Download

C H A P T E R 2Getting StartedIn this chapter, I am going to enhance the example web app I introduced in Chapter 1. These are theentry-level techniques, and most of the rest of the book is dedicated to showing you different ways toimprove upon the result. That’s not to say that the examples in this chapter are not useful; they areabsolutely fine for simple web apps. But they are not sufficient for large and complex web apps, which iswhy the chapters that follow explain how you can take key concepts from the world of server-sidedevelopment and apply them to your web apps.This chapter also lets me set the foundation for some web app development principles that I will beusing throughout this book. First, I will be relying on JavaScript libraries whenever possible so as toavoid creating code that someone else has produced and maintained. The library I will be making mostuse of is jQuery in order to make working with the DOM API simpler and easier (I explain some jQuerybasics in the examples in this chapters). Second, I will be focusing on a single HTML document.Upgrading the Submit ButtonTo get started, I am going to use JavaScript to replace the submit button from the baseline example inChapter 1. The browser creates this button from an input element whose type is submit, and I am goingto switch it out for something that is visually consistent with the rest of the document. More specifically,I am going to use jQuery to replace the input element.Preparing to Use jQueryThe DOM API is comprehensive but awkward to use—so awkward that there are a number of JavaScriptconvenience libraries that wrap around the DOM API and make it easier to use. In my experience, thebest of these libraries is jQuery, which is easy to use and actively developed and supported. jQuery is alsothe foundation for many other JavaScript libraries, some of which I’ll be using later. jQuery is just awrapper around the DOM API, and this allows the use of the underlying DOM objects and methods if itis required.You can download the jQuery library from jQuery.com. jQuery, like most JavaScript libraries, isavailable in two versions. The uncompressed version contains the full source code and is useful fordevelopment and debugging. The compressed version (also known as the minimized or minifiedversion) is much smaller but isn’t human-readable. The smaller size makes the minimized version idealfor saving bandwidth when a web app is deployed into production. Bandwidth can be expensive forpopular web apps, and any savings is worth making.Download the version you want and put it in your content directory, alongside example.html. I’ll beusing the uncompressed version in this book, so I have downloaded a file called jquery-1.7.1.js.15www.it-ebooks.info