Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

Chapter 9 ■ Data ValiDation teChniques
administrators, you’ll be amazed how often they can replace a 50-line switch/case or if/else construct you wrote in
JavaScript with a single regular expression. Many editing environments also feature “find” and “search and replace”
functionality, allowing the use of regular expressions.
Regular expressions are the cat’s pajamas once you get your head around them; however, at first sight a construct
like /^[\w]+(\.[\w]+)*@([\w]+\.)+[a-z]{2,7}$/i (which checks whether a string is a valid e-mail syntax) can
strike fear into the faint of heart. The good news is that it is not as tough as it looks.
Syntax and Attributes
Imagine you want to search for the string cat in text. You can define this as a regular expression in two different
formats:
// Expression literals; notice that you must not use quotation marks!
var searchTerm = /cat/;
// Object constructor
var searchTerm = new RegExp('cat');
If you use this expression on a string via the match(), search(), exec(), or test() method, it’ll return anything
that has “cat” in it—regardless of the location in the string—like catalog, concatenation, or scat.
If you want to match only the word “cat” as a string without anything else around it, you need to use a ^ to indicate
the start and a $ for the end:
var searchTerm = /^cat$/;
var searchTerm = new RegExp('^cat$');
You can also omit either the start indicator, ^, or the end indicator, $. This would match cat, catalog, or catastrophe:
var searchTerm = /^cat/;
var searchTerm = new RegExp('^cat');
The following code would find polecat or wildcat:
var searchTerm = /cat$/;
var searchTerm = new RegExp('cat$');
If you want to find “cat” regardless of case—for example, to match cat, Catherine, or CAT—you need to use the
i attribute following the second slash. This causes the case to be ignored:
var searchTerm=/cat/i;
var searchTerm=new RegExp('cat', 'i');
If you have a string that could have the word “cat” in it several times, and you want to get all matches as an array,
you need to add the parameter g for global:
var searchTerm = /cat/g;
var searchTerm = new RegExp('cat', 'g');
By default, regular expressions match patterns only in single-line strings. If you want to match a pattern in a
multiline string, use the parameter m for multiline. You can also mix them, and the order is not important:
var searchTerm = /cat/gim;
var searchTerm = new RegExp('cat', 'mig');
www.it-ebooks.info
281