get/decode/unescape parameters from URL using Javascript

Keywords:
GET decode unescape request parameter param URL javascript

Problem:
You need to get at the (GET) parameters in the URL of the window with some client-slide javascript. There's no built in mechanism to access these by name in an unencoded way so it would seem you have to parse the window location ... this must have been done by some one before.

Solution:
Found two good blogs that discuss this:

1. Get URL Parameters Using Javascript - uses regular expressions


2. Get parameters from URL with JavaScript - uses substrings from the location.search (ie the query portion of the URL)

I found the second approach easier to read, but both miss unescaping the parameter value once obtained ... there's a built in function for that. So here's what I've used:

<script type="text/javascript">
/*
 * Retrieves the query parameter with the given parameter name or empty 
 * string if not defined
 * 
 * @param parameter name of the parameter to retrieve
 */
function queryParam(parameter) {
    var searchString = top.location.search;
    searchString = searchString.substring(1);// ommit the leading '?'

    var paramValue = '';
    var params = searchString.split('&');
    for (i=0; i<params.length;i++) {
        var paramPair = params[i];
        var eqlIndex = paramPair.indexOf('=');
        var paramName = paramPair.substring(0,eqlIndex);
        
        if (paramName == parameter) {
            paramValue = unescape(paramPair.substring(eqlIndex+1));
            return paramValue;
        }
    }
    return paramValue;
}
</script>

So from a URL http://www.example.com/formprocess?name=Fred%20Bloggs&date=01%2f01%2f2008
You can get the unescaped parameter values via:

var name = queryParam('name'); // 'Fred Bloggs'
var date = queryParam('date'); // '01/01/2008' 

Notes:
This doesn't handle multi-valued parameters ... the first (regex) blog post has some comments on how to handle this.