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Simple Patterns

The patterns used in this chapter so far have all been simple, constructed of string literals. However, a

regular expression has many more parts than just matching specific characters. Metacharacters, charac-

ter classes, and quantifiers are all important parts of regular expression syntax and can be used to

achieve some powerful results.

Metacharacters

In the previous section you discovered that a comma has to be escaped (preceded with a backslash) to

be matched correctly. That’s because the comma is a

metacharacter

, which is a character that is part of

regular expression syntax. Here are all the regular expression metacharacters:

( [ { \ ^ $ | ) ? * + .

Any time you want to use one of these characters inside of a regular expression, they must be escaped.

So, to match a question mark, the regular expression looks like this:

var reQMark = /\?/;

Or like this:

var reQMark = new RegExp(“\\?”);

Did you notice the two backslashes in the second line? This is an important concept to grasp: When a

regular expression is represented in this (non-literal) form, every backslash must be replaced with two

backslashes because the JavaScript string parser tries to interpret

the same way it tries to interpret

To ensure that this doesn’t happen, place two backslashes (called

double escaping

) in front of the

metacharacter in question. This little

gotcha

is why many developers prefer to use the literal syntax.

Using special characters

You can represent characters by using their literals or by specifying a character code using either their

ASCII code or Unicode code. To represent a character using ASCII, you must specify a two-digit hexa-

decimal code preceded by

. For example, the character

has an ASCII code of 98, which is equal to

hex 62; therefore, to represent the letter

you could use

\x62

var sColor = “blue”;

var reB = /\x62/;

alert(reB.test(sColor)); //outputs “true”

In both of these methods, you may not see the advantage of using regular expres-

sions in place of simple strings. Keep in mind that the examples in this section of

the chapter are very simple and are used just for introducing concepts; more com-

plex patterns are discussed later and will truly show the power of using regular

expressions in place of simple strings.

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Regular Expressions

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