Adding/Modify query string / GET variables in a url with javascript

Question

So I am wanting to replace GET variable values in a url and if the variable does not exist, then add it to the url.

EDIT: I am doing this to a elements href not the pages current location..

I am not good with javascript but I do know how to use jQuery quite well and the basics of javascript. I do know how to write regex but not how to use the javascript syntax of regex and what functions to use it with.

Here is what I have so far and it does have an error on line 3: See it on jsfiddle(or below): http://jsfiddle.net/MadLittleMods/C93mD/

function addParameter(url, param, value) {
    var pattern = new RegExp(param + '=(.*?);', 'gi');
    return url.replace(pattern, param + '=' + value + ';');

    alert(url);
}

Answer 1

No need to use jQuery on this one. Regular Expressions and string functions are sufficient. See my commented code below:

function addParameter(url, param, value) {
    // Using a positive lookahead (?=\=) to find the
    // given parameter, preceded by a ? or &, and followed
    // by a = with a value after than (using a non-greedy selector)
    // and then followed by a & or the end of the string
    var val = new RegExp('(\\?|\\&)' + param + '=.*?(?=(&|$))'),
        parts = url.toString().split('#'),
        url = parts[0],
        hash = parts[1]
        qstring = /\?.+$/,
        newURL = url;

    // Check if the parameter exists
    if (val.test(url))
    {
        // if it does, replace it, using the captured group
        // to determine & or ? at the beginning
        newURL = url.replace(val, '$1' + param + '=' + value);
    }
    else if (qstring.test(url))
    {
        // otherwise, if there is a query string at all
        // add the param to the end of it
        newURL = url + '&' + param + '=' + value;
    }
    else
    {
        // if there's no query string, add one
        newURL = url + '?' + param + '=' + value;
    }

    if (hash)
    {
        newURL += '#' + hash;
    }

    return newURL;
}

And here is the Fiddle

Update:

The code now handles the case where there is a hash on the URL.

Edit

Missed a case! The code now checks to see if there is a query string at all.

Answer 2

I would go with this small but complete library to handle urls in js:

https://github.com/Mikhus/jsurl