Why array.push() is used to make an object?

Question

I was reading How can I get query string values in JavaScript? on Stackoverflow and this piece of code from the first reply made me wonder why ´vars.push()´ is used like this?

function getUrlVars()
{
    var vars = [], hash;
    var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');
    for(var i = 0; i < hashes.length; i++)
    {
        hash = hashes[i].split('=');
        vars.push(hash[0]);
        vars[hash[0]] = hash[1];
    }
    return vars;
}

But instead of this:

var vars=[];
...
vars.push(hash[0]);
vars[hash[0]] = hash[1];

I rewrote the code like:

var vars={};
...
vars[hash[0]] = hash[1];

and it works. Now the questions are:

• why would someone use an array for that kind of reply?
• and why would someone use ARR.push(KEY) and then use ARR[KEY]=VAL format afterwards?

Answer 1

This results in vars being both an array of keys and a dictionary.
The only good reason I can think of is to keep the order of the query parameters, which is not defined in a dictionary.

Either way, I would note this function removes duplicated query parameters - it only keeps the last value (though the key would be inserted multiple times to the array)