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

Logical operators


There are three operators, called logical operators, that work with Boolean values. These are:

  • ! – logical NOT (negation)

  • && – logical AND

  • || – logical OR

You know that when something is not true, it must be false. Here's how this is expressed using JavaScript and the logical ! operator:

> var b = !true;
> b;
false

If you use the logical NOT twice, you get the original value:

> var b = !!true;
> b;
true

If you use a logical operator on a non-Boolean value, the value is converted to Boolean behind the scenes:

> var b = "one";
> !b;
false

In the preceding case, the string value "one" is converted to a Boolean, true, and then negated. The result of negating true is false. In the next example, there's a double negation, so the result is true:

> var b = "one";
> !!b;
true

You can convert any value to its Boolean equivalent using a double negation. Understanding how any value converts to a Boolean is important. Most values convert to true with the exception...