Null,undefined and empty applications in JavaScript

Function demo () {    alert (typeof a ==  "undefined");//true}function  demo () {    alert (a == null);//console error a is not  defined}function demo (a) {    alert (typeof a ==  "undefined");// True    alert (A == null);//true}function demo () {    var  a;    alert (typeof a ==  "undefined");//true     alert (a == null);//true}function demo () {    var a= document.getElementById ("name"). Value;//this node  exists! but it has no  value    alert (a ==  "");//true    alert (a ==  null);//false    alert (typeof a ==  "undefined");//false}function  demo () {    var a=documEnt.getelementbyid ("name"). Value;//this node is not here    alert (A  ==  "");//false    alert (A == null);//true     Alert (typeof a ==  "undefined"),//false}function () {    alert (null ==  undefined)//true    //using the TypeOf method, as mentioned earlier, NULL is not the same as the type of undefined, so the output is "false". and the = = = Absolute equals, here null === undefined output false.     alert (null === undefined);//false    alert (typeof  null == typeof undefined);  //false}

Null,undefined and empty applications in JavaScript