Entry

How do I match a regexp pattern with a string?

How do I test if a certain pattern is contained in a given string?

Oct 6th, 2006 12:51
Daniel LaLiberte, Rey Nuņez,

JavaScript 1.2 includes two methods for these:
- the regexp.test() method, which returns a Boolean value that 
indicates whether or not a pattern exists in a searched string, and;
- the string.match() method, which returns, as an array, the results 
of 
a search on a string using a supplied regular expression object.
Typical syntax is:
  pattern.test(string)
  string.match (/pattern/modifiers)
Typically, the test method, which returns true if the regular 
expression exists within the string, is used to direct program flow. 
var found = pattern.test(str)
if (found)
  // a match occurred
else
  // no match occurred
The sample below shows a simple use of the match method. The function 
returns an array of the match(es) found, if successful, and null 
otherwise. 
<script language="JavaScript1.2">
<!--
function matchMe(re, str) {
var pattern = new RegExp (re,'ig');
alert (str.match(pattern))
}
//-->
</script>
To test, type different patterns to match in the first text box, and 
the test string in the second. 
<div align="center">
<form onsubmit="matchMe(re.value, test.value); return false">
<table cellpadding=10 cellspacing=0 border=0 bgcolor="khaki">
<tr>
  <td>Match pattern:<br><input name="re"></td>
  <td>Test string:<br><input name="test"></td></tr>
<tr>
  <td colspan=2 align="center"><input type="submit" 
value="Match"></td></tr>
</table></form></div>
If you use a regular expression stored in a variable more than once, 
be sure to reset the lastIndex property to 0 after each match (or 
before the next match).  Otherwise the next match will start at the 
character position of the end of the previous match.
  var pattern = /java/i;
  pattern.test("JavaScript");  // Returns true
  pattern.lastIndex = 0;
  pattern.test("ECMAScript");  // Returns false