↑
Main Page

Quantifiers

Code Equal To

Matches

[^\t\n\x0B\f\r]

A non-white–space character

[a-zA-Z_0-9]

A word character (all letters, all numbers, and an underscore)

[^a-zA-Z_0-9]

A non-word character

Using predefined classes can make pattern matching significantly easier. Suppose you want to match

three numbers, without using

. Your code looks like this:

var sToMatch = “567 9838 abc”;

var reThreeNums = /[0-9][0-9][0-9]/;

alert(reThreeNums.test(sToMatch)); //outputs “true”

Using

, the regular expression becomes much cleaner:

var sToMatch = “567 9838 abc”;

var reThreeNums = /\d\d\d/;

alert(reThreeNums.test(sToMatch)); //outputs “true”

Quantifiers

Quantifiers enable you to specify how many times a particular pattern should occur. You can specify

both hard values (for example, this character should appear three times) and soft values (for example,

this character should appear at least once but can repeat any number of times) when setting how many

times a pattern should occur.

Simple quantifiers

The following table lists the various ways to quantify a particular pattern.

Code Description

Either zero or one occurrence

Zero or more occurrences

One or more occurrences

{

}

Exactly

occurrences

{

}

At least

but no more than

occurrences

{

}

At least

occurrences

For example, suppose you want to match words

bread

read

, or

red

. Using the question mark quantifier,

you can create just one regular expression to match all three:

var reBreadReadOrRed = /b?rea?d/;

201

Regular Expressions

10_579088 ch07.qxd 3/28/05 11:38 AM Page 201