Now that you know what a regular expression is, let's look at using it in a script. JavaScript's String object exposes a number of methods that support regular expressions. The first of these is the search() method, used to search a string for a match to the supplied regular expression. Take a look at the next example:


<script language="JavaScript">
 
// define string to be searched
var str = "The Matrix";
 
// define search pattern
var pattern = /trinity/;
 
// search and return result
if(str.search(pattern) == -1) 
{
 alert("Sorry, Trinity is not in The Matrix.");
} else 
{
 alert("Trinity located in The Matrix at character " + 
str.search(pattern));
}
 
</script>



When you run this script, you should see the following:

Sorry, Trinity is not in The Matrix.

The search() method returns the position of the substring matching the regular expression, or -1 if no match exists. In the example above, it is clear that the pattern "trinity" does not exist in the string "The Matrix," hence the error message.

Now, look what happens when I update the regular expression so that it results in a positive match:


<script language="JavaScript">
 
// define string to be searched
var str = " The Matrix";
 
// define search pattern
var pattern = /tri/;
 
// search and return result
if(str.search(pattern) == -1) 
{
 alert("Sorry, Trinity is not in The Matrix.");
} else 
{
 alert("Trinity located in The Matrix at character " + 
str.search(pattern));
}
 
</script>



This time round, the JavaScript interpreter will return a match (and the location where it found the match). Here's the output:

Trinity located in The Matrix at character 7