Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

Chapter 9 ■ Data Validation Techniques
For example, if you want to test for a US Social Security number, which is a nine-digit number with dashes following
the third and the fifth digits (for example, 456-33-1234), you can use the following regular expression, with optional
dashes (using the ? quantifier), because the user might not enter them:
var searchTerm = /[0-9]{3}\-?[0-9]{2}\-?[0-9]{4}/;
var searchTerm = new RegExp('[0-9]{3}\-?[0-9]{2}\-?[0-9]{4}', ");
Alternatively, you can use the shortcut notation for digits:
var searchTerm = /\d{3}\-?\d{2}\-?\d{4}/;
var searchTerm = new RegExp('\\d{3}\-?\\d{2}\-?\\d{4}', ");
Be aware that if you use the shortcut notations inside quotation marks or in the constructor notation, you need
to precede them with double backslashes, not single ones, because you need to escape them! With this knowledge,
you should be well equipped to write your own regular expressions. As proof, let’s go back to the example in the
beginning paragraph of this section:
var validEmail = /^[\w]+(\.[\w]+)*@([\w]+\.)+[a-z]{2,7}$/i
E-mails can be pretty straightforward, like me@example.com, or more complex, like
chris.heilmann.webdev@example.museum. This regular expression should return both as valid e-mails.
It tests whether the string starts with a group of one or more word characters, ^[\w]+, followed by a group of 0
or more word characters preceded by a period, (\.[\w]+)*, before the @ sign. After the @ sign, the string might have
one or more groups of one or more word characters followed by a period, ([\w]+\.)+, and it’ll end in a string that has
between two and seven characters. This last string is the domain, which could be something short like de or longer
like name or museum. Notice that by allowing several words followed by a period, you also make sure that e-mails like
user@open.ac.uk are recognized.
Methods Using Regular Expressions
There are several methods that take regular expressions as parameters. The expression itself—the things inside the
slashes or the RegExp constructor—is called a pattern, because it matches what you want to retrieve or test for.
• instance.test(string): Tests whether the string matches the pattern, and returns true
or false.
• instance.exec(string): Matches the string and the pattern one time, and returns an array of
matches or null.
• instance.match(pattern): Matches the string and the pattern, and returns the resulting
matches as an array of strings or null.
• instance.search(pattern): Matches the string and the pattern, and returns the positions of
the positive matches. If the string does not match any of the pattern, the search returns –1.
• instance.replace(pattern, replaceString): Matches the string against the pattern, and
replaces every positive match with replaceString.
• instance.split(pattern, limit): Matches the string against the pattern, and splits it into
an array with the substrings surrounding the pattern matches as array items. The optional
limit parameter cuts down the number of array elements.
284
www.it-ebooks.info