I'm trying to read some specific values from a string.

elementName = "item add item:mk0090 destination:project1";

 You can see there two  key:value  pairs. How can I find this value knowing an key ?

Matching 'item:mk0090' or 'destination:project1' is easy:

elementID.match( '/\b' + 'item' + ':[A-Z0-9]\b/', elementName);

==> item:mk0090

but how to capture for corresponding item value or destination value with regular expression which works also with IE6 (starting at Javascript 1.3) ?

Please help !

Please be more specific about your goal, if it is to reference the matched colon-separated values in that string:

Raw Match Pattern:
([^ ]*):([^ ]*)

Javascript Code Example:
<script type="text/javascript">
  var re = /([^ ]*):([^ ]*)/g;
  var sourcestring = "source string to match with pattern";
  var results = new Array();
  var ii = 0;
  for (var matches = re.exec(sourcestring); matches != null; matches = re.exec(sourcestring)) {
    results[ii] = new Array();
    for (var j=0; j<matches.length; j++) {
      results[ii][j]=matches[j];
      alert("results["+ii+"]["+j+"] = " + results[ii][j]);
    }
    ii++;
  }
</script>

$matches Array:
(
    [0] => Array
        (
            [0] => item:mk0090
            [1] => destination:project1
        )

    [1] => Array
        (
            [0] => item
            [1] => destination
        )

    [2] => Array
        (
            [0] => mk0090
            [1] => project1
        )

)

Thank you for your assistance !

More specific goal is find VALUE knowing a KEY from STRING.

sampleString =  "source_string_to_KEY1:VALUE1_match_with_pattern_KEY2:VALUE2"

So for example I need to capture (only) VALUE1 when i know only KEY1 from that sampleString.

Key:Value pairs are with colon-separated form. All words are underline-separated in that string. String is used in DOM Element ID name.

Yes, I can solve this with unskilful string handling. Like splitting string by '_' to substrings, finding stings, that contains ':', then comparing first part of this substring with knowing key and finally return last part as a match.

Probably there is possibility find this match simply with regular expression. This regex should find this key:value pair but only capture required value part. Is there any possibility ?

This is my goal.
 

I used now your excellent tester at myregextester.com and my best result is:

Source text:

source_string_to_KEY1:VALUE1_match_with_pattern_KEY2:VALUE2 

Raw Match Pattern:
(?=KEY1:([^_]*))

$matches Array:
(
    [0] => 
    [1] => VALUE1
)

This solution does'nt work with IE6 (below JS 1.5) 

But I'm looking for something like:

$matches Array:
(
    [0] => VALUE1
) 

Which works with IE6 (JS 1.3)