parseQueryString.js

// Handles also array params well
function parseQueryString(query) {
    var pars = (query != null ? query : "").replace(/&+/g, "&").split('&'),
        par, key, val, re = /^([\w]+)\[(.*)\]/i, ra, ks, ki, i = 0,
        params = {};

    while ((par = pars.shift()) && (par = par.split('=', 2))) {
        key = decodeURIComponent(par[0]);
        // prevent param value going to be "undefined" as string
        val = decodeURIComponent(par[1] || "").replace(/\+/g, " ");
        // check array params
        if (ra = re.exec(key)) {
            ks = ra[1];
            // init array param
            if (!(ks in params)) {
                params[ks] = {};
            }
            // set int key
            ki = (ra[2] != "") ? ra[2] : i++;
            // set array param
            params[ks][ki] = val;
            // go on..
            continue;
        }
        // set param
        params[key] = val;
    }

    return params;
}

var query = 'foo=1&bar=The+bar!%20&arr[]=a0&arr[]=a1&arr[s]=as&isset&arr[]=last';
var params = parseQueryString(query);
console.log(params)
console.log(params.foo)        // 1
console.log(params.bar)        // The bar!
console.log(params.arr[0])     // a0
console.log(params.arr[1])     // a1
console.log(params.arr.s)      // as
console.log(params.arr.none)   // undefined
console.log("isset" in params) // true like: isset($_GET['isset'])


/*
// in php
parse_str('foo=1&bar=The+bar!%20&arr[]=a0&arr[]=a1&arr[s]=as&isset&arr[]=last', $query);
print_r($query);

Array
(
    [foo] => 1
    [bar] => The bar!
    [arr] => Array
        (
            [0] => a0
            [1] => a1
            [s] => as
            [2] => last
        )

    [isset] =>
)*/