Understanding Regular Expressions - HTML, CSS, and Dynamic HTML - page 1163

Another useful technique in regular expressions is to group character symbols. Once
you create a group, the symbols within that group can be treated as a single unit. The
syntax to create a group is
( pattern )
where pattern is a regular expression pattern. For example, a phone number might be
entered with or without an area code. The pattern for a phone number without an area
code, matching such numbers as 555-1234 , is
/^\d{3}-\d{4}$/
If an area code is included in the format 800-555-1234 , the pattern is
/^\d{3}-\d{3}-\d{4}$/
To allow the area code to be added, you place it within a group and use the ? repetition
character applied to the entire area code group. The regular expression is thus
/^(\d{3}-)?\d{3}-\d{4}$/
which matches either 555-1234 or 800-555-1234 .
Working with the Regular Expression Object
Now that you have reviewed the syntax involved in writing a regular expression, you can
use regular expressions in JavaScript programs. As noted earlier, a regular expression is
treated as an object with its own collection of properties and methods.
Exploring Regular Expression Methods
One method associated with regular expressions is the test() method, which is used to
determine whether a text string contains a substring that matches the pattern defined by a
regular expression. The syntax of the test() method is
re .test( string )
where re is a regular expression object and string is the text string you want to test.
The test() method returns the Boolean value true if a match is located within the text
string and false otherwise. For example, the following code uses the test() method to
compare the text string stored in the zipstring variable with the regular expression object
stored in the regx variable:
var zipstring = document.forms[0].zip.value;
var regx = /^\d{5}$/;
var testvalue = regx.test(zipstring);
If zipstring matches the pattern, the testvalue variable will have a value of true ; other-
wise, it will have a value of false. If you need to know where within the text string the
match occurs, you can use the following search() method:
re .search( string )
The search() method returns the index of the first matching substring from string . If
no match is found, it returns the value -1. All searches occur from the start of the text
string.
You can also use regular expression methods that extract substrings from a text string.
The match() method creates an array of substrings from a text string that match the pat-
tern defined in a regular expression. The syntax of the match() method is
results = re .match( string )