js null undefined null difference explanation_javascript skills

null, the object does not exist
var ii= document.getElementById("id");
alert(ii);
The id object does not exist on the current page

undefined
var i;
alert(i);
The declared variable is not initialized
alert(document.oiji); >

Empty

var iab = document.getElementById("name").value; alert(iab);
id= The value of name is empty