Query String parsing: Handling both & and ;

I've found plenty of articles on StackOverflow that mention fast ways to parse query string's in Javascript, but what I haven't found is how to handle both & and ; as a delimiter.

Now, I assume, only one of those gets set as the delimiter for the query string. Take for instance, the following query string:

index.php?Param1=value&Param2=value;Param3=value

Which is the delimiter?

• Is it &, or is it ;?
• Is it the first recognized delimiting character, or is it & takes precedence over ;?
• Are both treated as delimiters, and all three parameters from the example parsed?

In Javascript, I have historically been using the following function:

/**
 * Gets the value of a parameter from a URI.
 * @param href The full URI to search. Must at least start with a ? query string delimiter.
 * @param key  The key of the param for which to retrieve the value.
 * @param def  A default value to return in the case that the key cannot be found in the query string.
 * @return The value of the param if the key is found, otherwise returns def.
 */
function getURIParam(href, key, def) {
    if (arguments.length == 2) def = null;

    var qs = href.substring(href.indexOf('?') + 1);
    var s = qs.split('&');
    for (var k in s) {
        var s2 = s[k].split('=');
        if (s2[0] == key)
            return decodeURIComponent(s2[1]);
    }

    return def;
}

That just splits out each key/value pair based on &. It works great, so long as the delimiter is always &. As we know, however, that is not always the case, nor should be enforced, as the RFC allows for ; as well.

So, in order to handle both & and ; as a delimiter, should I first search for an indexOf("&") and if no occurrence is found, set the delimiter to ;?

What is the proper way of parsing a URL based on the rule that the delimiter can be either & or ;?

Here is the W3C Recommendation on server being able to handle both & and ;.

We recommend that HTTP server implementors, and in particular, CGI implementors support the use of ";" in place of "&" to save authors the trouble of escaping "&" characters in this manner.

Here is RFC 1738 which defines the URI.