Regular expressions in JS

[poizn]

Hi all

Im having a little problem with a regular expressions. Here is the code

  var pattern = new RegExp("(^|\s)match_me(\s|$)");

  if(pattern.test("match_me something_else"))
    alert('match');
  else
    alert('no match');

I cant figure out why this doesn't work, well to my understanding this should work...
Iv also tried

  var pattern = new RegExp("(^|\s|\b)match_me(\b|\s|$)");

And it also doesn't work.

Can anyone help?
Thanks in advance

[poizn]

Hi. I have sort of got it to work, but with some new problems

If I create the pattern without inverted commas " it works, like so

  var pattern = /\bmatch_me\b/;

  if(pattern.test("match_me something_else"))
    alert('match');
  else
    alert('no match');

This will match, but the pattern needs to be dynamic (ie. match_me could be anything)

So how can I create the pattern dynamically?

[poizn]

Hi again for the 3rd and hopefully last time.

I got it

Change the pattern to the following

  var search_for = 'match_me';
  var pattern = new RegExp("\\b" + search_for + "\\b");

And it works

[paul_wilkins]

You shouldn't use \b to find the word breaks because that includes other word separators, like the hyphen or underscore, which means that match_me will also match match_me_now

Going from your original code, if you don't need a custom string in the regex then you should regex delimiters instead of building one from a string.

If you do create a new regex object, then you'll need to escape any slashes that you have in there.

// The preferred method
var pattern = /(^|\s)match_me(\s|$)/;
// Or, with a custom string
var pattern = new RegExp('(^|\\s)' + text + '(\\s|$)');