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Comment by chmod775 | Hacker News Reader

He missed an opportunity to make that even shorter and even more of a clusterfuck.

I present to you:

    function compress(data){
        var s = {}, q = [];
        data.replace(/([^=&]+)=([^&]*)/g, function(m, k, v) {
            s[k] ? q[s[k] - 1] += "," + v : s[k] = q.push(m);
        });
        return q.join("&");
    }

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Further fucked:

        function compress(data){
            return data.replace(/(?<=(\w+)=[^&]*)&\1=/g,',');
        }

I say: do replace after all!

(Javascript didn't have zero-width look-behinds at the time)

That doesn't handle strings like

    foo=1&foo=2&foo=3&blah=a&blah=b&foo=4

correctly. You'd expect

    foo=1,2,3,4&blah=a,b

but get

    foo=1,2,3&blah=a,b&foo=4

I don't think it's possible to solve this just using a single search/replace.

It wasn't clear from the post whether that was a valid input. If it is, some parts would need to be re-ordered, making it a very fancy search/replace indeed. But I still think it's possible. One or two replacements to switch the ordering, and then my original one to get the final output.

I put some effort into trying to find a search/replace to do it. Without a high-powered replacement function, I couldn't do it. But I did do this instead.

        function compress(data){
            return data.split`&`.sort().join`&`.replace(/(?<=(\w+)=[^&]*)&\1=/g,',');
        }

That's a really creative way to do it!

I think he avoided the array + join on purpose and went directly for final string concatenation :)

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