A query string is an optional part of a URL that goes after the file name and begins with a question mark (?). For example, the following URL has a query string ?quryEg after the HTML file name: http://www.findnerd.com/file.html?quryEg

Here is an example code to get the query string values:-

<script type="text/javascript">
function getquryvalues (querystring) {
    name = querystring.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");
    var regexS = "[\\?&]" + name + "=([^&#]*)";
    var regex = new RegExp(regexS);
    var results = regex.exec(window.location.search);
    if (results == null) {
        return "";
    }
    else {
        return decodeURIComponent(results[1].replace(/\+/g, " "));
    }
}

var userid = getquryvalues('userid');
var username = getquryvalues('username');
</script>

In the above code regex.exec test for a match in the string and decodeURIComponent is used to decode the URI component.

This is how you can use this code to get the query string value using javascript.