Array reduce example to convert a query-string to parameter object (requires EcmaScript 5)

deparam.js

var queryString = "foo=bar&a=b%C3%B8";
var decode = decodeURIComponent;

var paramObj = queryString.split("&").reduce(function (obj, pair) {
    var keyVal = pair.split("=");
    var key = keyVal[0];
    var val = keyVal[1];

    obj[ decode(key) ] = decode(val);
    return obj;
}, {}); // initial value for obj

// paramObj == {foo: "bar", a: "bø"}