Preface

Regular expressions are patterns or templates, which allow you to define a set of rules in a natural yet vague way, giving you the ability to match and validate text. They have, more or less, been implemented in nearly every modern programming language.

When working with any type of textual input, you don't always know what the value will be, but you can usually assume (or even demand) the format you are going to receive into your application. These types of situations are exactly when you would create a regular expression to extract and manipulate this input.

In this book, you will learn the basics to get started with a regular expression in JavaScript. We will start with the basics, passing through some special patterns and then, dive into two examples. The first one is validating a web form, and the second one is a very complex pattern to extract information from a log file. For all the examples, we will use a step-by-step approach, which will make it easier to learn and assimilate all the knowledge we've gained from this book.