JavaScript Cookbook

Chapter 2. Using Regular Expressions

2.0. Introduction

Regular expressions are search patterns that can be used to find text that matches a given pattern. For instance, in the last chapter, we looked for the substring Cookbook within a longer string:

var testValue = "This is the Cookbook's test string";
var subsValue = "Cookbook";

var iValue = testValue(subsValue); // returns value of 12, index of substring

This code snippet worked because we were looking for an exact match. But what if we wanted a more general search? For instance, we want to search for the words Cook and Book, in strings such as “Joe’s Cooking Book” or “JavaScript Cookbook”?

When we’re looking for strings that match a pattern rather than an exact string, we need to use regular expressions. We can try to make do with String functions, but in the end, it’s actually simpler to use regular expressions, though the syntax and format is a little odd and not necessarily “user friendly.”

Recently, I was looking at code that pulled the RGB values from a string, in order to convert the color to its hexadecimal format. We’re tempted to just use the String.split function, and split on the commas, but then you have to strip out the parentheses and extraneous whitespace. Another consideration is how can we be sure that the values are in octal format? Rather than:

rgb (255, 0, 0)

we might find:

rgb (100%, 0, 0)

There’s an additional problem: some browsers return a color, such as a background color, as an RGB value, others as a hexadecimal. ...