QueryString Javascript collection object capable of handling arrays

Question

I need to take a query string (example: ?name=value1&type=value2&name=value3&type=value4... but this code should be able to handle any query string passed to it) and create an object from it.

I have nearly completed a function that does this. However, my logic is a bit off inside that last for loop. If someone could please point out where I've gone wrong I'd really appreciate it!

First I grab the query string using jQuery's $.get function:

$.get("xmlreader.php", function(data) { 

    var queryParams = [];

    var qString = data;

    // test qString for & at the end
    var last = qString.lastIndexOf("&");
    if(last == qString.length - 1) {
        // then there is a & to remove
        qString = qString.substring(0,qString.length-1);
    }

    getParamObj(qString);

});

(I know it's funky that I remove the last & here in my JavaScript but I don't want to focus on that here at all.)

Then I call getParamObject(qString); to build the actual collection object:

function getParamObj(parameterString) {

var qString = parameterString;
var parameters = qString.split("&");
parameters[0] = parameters[0].substring(1);

var paramObject = new Object();

for(var index = 0; index < parameters.length; ++index) {
    var equalsPos = parameters[index].indexOf("=");
    var key = parameters[index].substring(0,equalsPos);

    var stringLength = parameters[index].length;

    var value = parameters[index].substring(equalsPos + 1, stringLength);

    if(!paramObject[key]) {
        console.log("paramObject[key] = " + paramObject[key]);
        paramObject[key] = value;
        if(paramObject[key] instanceof Array ) {
            console.log("instance of array");
            paramObject[key].push(value);
        }  else {
            var newArray = [];
            var existingValue = paramObject[key];
            console.log("existing value: " + existingValue);
            console.log("value: " + value);
            newArray.push(existingValue);
            newArray.push(value);
            paramObject[key] = newArray;
        }   

    }

}

The function is working -almost- correctly. A couple things are wrong when I test it: in the last conditional existingValue and value are the same. There may be other issues as well but I think that's the primary one.

I've seen approaches that use regular expressions but I DON'T want to take that route here.

Note: I've answered my own question LOL... stack won't let me comment this because I'm not cool enough yet at just 58 rep :)

[code]
if(!paramObject[key]) {
    console.log("paramObject[key] = " + paramObject[key]);
    paramObject[key] = value; 
    console.log("paramObject[key] = value = " + value + paramObject[key]);
    console.log(paramObject[key]);
    }
    else if(paramObject[key] instanceof Array ) {
    paramObject[key].push(value);
    console.log("value if arra" + value);
    }  else {
    var newArray = [];
    var existingValue = paramObject[key];
    console.log("existing value: " + existingValue);
    console.log("value: " + value);
    newArray.push(existingValue);
    newArray.push(value);
    paramObject[key] = newArray;
    }
[/code] 

Answer 1

Although you say you don't want a regex-based implementation, I thought it would be helpful to show what it can look like:

params = {}
queryString.replace(/([^&=]+)=([^&=]*)/g, function($0, $1, $2) {
    (params[$1] = params[$1] || []).push($2);
});
// that's basically all about this

(Doesn't answer the question, hence CW).