Book Image

Object-Oriented JavaScript - Second Edition

Book Image

Object-Oriented JavaScript - Second Edition

Overview of this book

JavaScript is the behavior, the third pillar in today's paradigm that looks at web pages as something that consists of clearly distinguishable parts: content (HTML), presentation (CSS) and behavior (JavaScript). Using JavaScript, you can create not only web pages but also desktop widgets, browser and application extensions, and other pieces of software. It's a pretty good deal: you learn one language and then code all kinds of different applications. While there's one chapter specifically dedicated to the web browser environment including DOM, Events and AJAX tutorials, the rest is applicable to the other environments Many web developers have tried coding or adopting some bits of JavaScript, but it is time to "man up" and learn the language properly because it is the language of the browser and is, virtually, everywhere. This book starts from zero, not assuming any prior JavaScript programming knowledge and takes you through all the in-depth and exciting futures hidden behind the facade. Once listed in the "nice to have" sections of job postings, these days the knowledge of JavaScript is a deciding factor when it comes to hiring web developers. After reading this book you'll be prepared to ace your JavaScript job interview and even impress with some bits that the interviewer maybe didn't know. You should read this book if you want to be able to take your JavaScript skills to a new level of sophistication.
Table of Contents (19 chapters)
Object-Oriented JavaScript Second Edition
Credits
About the Authors
About the Reviewer
www.PacktPub.com
Preface
Built-in Functions
Regular Expressions
Index

Closures


The rest of the chapter is about closures (what better way to close a chapter?). Closures can be a little hard to grasp initially, so don't feel discouraged if you don't "get it" during the first read. You should go through the rest of the chapter and experiment with the examples on you own, but if you feel you don't fully understand the concept, you can come back to it later when the topics discussed previously in this chapter have had a chance to sink in.

Before moving on to closures, let's first review and expand on the concept of scope in JavaScript.

Scope chain

As you know, in JavaScript, there is no curly braces scope, but there is function scope. A variable defined in a function is not visible outside the function, but a variable defined in a code block (for example an if or a for loop) is visible outside the block:

> var a = 1; 
> function f() {
    var b = 1; 
    return a;
  }
> f();
1
> b;
ReferenceError: b is not defined

The variable a is in the global space...