How to get Query String using javascript

query-string.js

/**
* @description Below function will return a object of query string variable
**/
var QueryString = function () {
  // This function is anonymous, is executed immediately and 
  // the return value is assigned to QueryString!
  var query_string = {};
  var query = window.location.search.substring(1);
  var vars = query.split("&");
  for (var i=0;i<vars.length;i++) {
    var pair = vars[i].split("=");
        // If first entry with this name
    if (typeof query_string[pair[0]] === "undefined") {
      query_string[pair[0]] = decodeURIComponent(pair[1]);
        // If second entry with this name
    } else if (typeof query_string[pair[0]] === "string") {
      var arr = [ query_string[pair[0]],decodeURIComponent(pair[1]) ];
      query_string[pair[0]] = arr;
        // If third or later entry with this name
    } else {
      query_string[pair[0]].push(decodeURIComponent(pair[1]));
    }
  } 
  return query_string;
}();

/*
* @description Below function will return parameter by name
* @param name of query strring variable
* @param url having query string
*/
function getParameterByName(name, url) {
    if (!url) url = window.location.href;
    url = url.toLowerCase();
    name = name.replace(/[\[\]]/g, "\\$&").toLowerCase();
    var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
        results = regex.exec(url);
    if (!results) return null;
    if (!results[2]) return '';
    return decodeURIComponent(results[2].replace(/\+/g, " "));
}

/*
* @description Remove query string variable
* @param url having query string
* @param parameter to remove form query string
*/
function removeURLParameter(url, parameter) {
    //prefer to use l.search if you have a location/link object
    var urlparts= url.split('?');
    if (urlparts.length>=2) {

        var prefix= encodeURIComponent(parameter)+'=';
        var pars= urlparts[1].split(/[&;]/g);

        //reverse iteration as may be destructive
        for (var i= pars.length; i-- > 0;) {
            //idiom for string.startsWith
            if (pars[i].lastIndexOf(prefix, 0) !== -1) {
                pars.splice(i, 1);
            }
        }
        url= urlparts[0] + (pars.length > 0 ? '?' + pars.join('&') : "");
        return url;
    } else {
        return url;
    }
}