JavaScript compensating for RegExp global non capturing groups

gistfile1.js

//author: lo sauer 2011
//given for instance, is a text with placeholders of which only the value is to be captured
//JS's 'match' ignores the non-capture group (?:...), for instance in a global search
str = "Hello I am {{name}}. Is it already the {{date}}";

str.match(/(?:\{{2})([a-z0-9]*)(?:\}{2})/i);
>>>["{{name}}", "name"]

str.match(/(?:\{{2})([a-z0-9]*)(?:\}{2})/gi);
>>>["{{name}}", "{{date}}"]

str.match(/\{{2}([a-z0-9]*)\}{2}/gi);
>>>["{{name}}", "{{date}}"]

//two solutions
//1.solution (for phptrim see here https://gist.github.com/1260006 )
str.match(/\{{2}([a-z0-9]*)\}{2}/gi).map(function(e){return e.phptrim('{}'); });
>>>["name", "date"]

//2.solution
var rexp = /\{{2}([a-z0-9]*)\}{2}/gi;
var matches = [];
while (m = rexp .exec(str)) 
{
    matches.push(m[m.length-1]);
};