how to display page on valid query string in javascript code example

Example 1: javascript reading query parameter

// example url: https://mydomain.com/?fname=johnny&lname=depp
const urlParams = new URLSearchParams(window.location.search);
const firstName = urlParams.get('fname'); // johnny

Example 2: javascript get query parameter

function getUrlParameter(name) {
    name = name.replace(/[\[]/, '\\[').replace(/[\]]/, '\\]');
    var regex = new RegExp('[\\?&]' + name + '=([^&#]*)');
    var results = regex.exec(location.search);
    return results === null ? '' : decodeURIComponent(results[1].replace(/\+/g, ' '));
};