Parse values out of paramaterized strings in javascript

Question

Say I have a string, such as:

var map = "/directory/:id/thumbnails/:size";

And I want to use that to map against another string (essentially, the same thing that Rails uses to define Routes), such as:

var str = "/directory/10/thumbnails/large";

I would like to "compare" the two strings, and return a Key-Value Pair or JSON Object that represents the parts of str that map to map, which in my example above, would look like:

obj = {
    'id'   : '10',
    'size' : 'large'
}

Would this be a good fit for JavaScript Regex? Can anyone help me?

any good reason to be doing that with javascript instead of a server-side language? — yoda
– yoda, Commented Jan 31, 2011 at 4:31
I'm not actually using it for routing, that was just the most convenient example, since it's what everyone is likely familiar with. — Mike Trpcic
– Mike Trpcic, Commented Jan 31, 2011 at 4:33
Yes, it's possible. You can use a regexp to convert the map into a regexp, and then use that regexp to parse the string in question. — Jason LeBrun
– Jason LeBrun, Commented Jan 31, 2011 at 4:35
Every time you say "JSON object," a ninja cuts off a baby animal's head. Please think of the cute widdle aminals, and use the right terminology. — Matt Ball
– Matt Ball, Commented Jan 31, 2011 at 4:39

Darko · Accepted Answer · 2011-01-31 04:47:27Z

I found it easier to just write the code for this than to explain :)

var map = "/directory/:id/thumbnails/:size";
var str = "/directory/10/thumbnails/large";

var obj = {};

var mapArr = map.split('/');
var strArr = str.split('/');

if (mapArr.length != strArr.length) return false;

for (var i = 0; i < mapArr.length; i++)
{
    var m = mapArr[i];
    var s = strArr[i];

    if (m.indexOf(":") != 0) continue;

    m = m.substring(1);    
    obj[m] = s;
    document.write(m + " = ");
    document.write(obj[m]);
    document.write("<br/>");
}

You can also see it in action here => http://jsfiddle.net/5qFkb/

Do ask if you have any questions, but the code should be self-explanatory. Also be aware that there is no usual null checking and stuff I'd usually put in - this is just meant as a quick and dirty proof of concept.

Oh and in case it wasn't clear from my answer; no, I wouldn't use regex, because then I'd have two problems instead of one.

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