Get the query string value and display it in my html page

Question

I can see the query string values that I had entered on the previous page after being sent to the home.html page.

Home.html?FirstName=dd&LastName=ee&smtButton=Submit

And am getting the result:

firstname = undefined
lastname = undefined
age = undefined

Could anyone help me to solve this?

JS:

function getParams() {
    var idx = document.URL.indexOf('?');
    var params = new Array();
    if (idx != -1) {
        var pairs = document.URL.substring(idx + 1, document.URL.length).split('&');
        for (var i = 0; i < pairs.length; i++) {
            nameVal = pairs[i].split('=');
            params[nameVal[0]] = nameVal[1];
        }
    }
    return params;
}

params = getParams();
firstname = unescape(params["firstname"]);
lastname = unescape(params["lastname"]);
age = unescape(params["age"]);
document.write("firstname = " + firstname + "<br>");
document.write("lastname = " + lastname + "<br>");
document.write("age = " + age + "<br>");