define a obj with var keyword and without

var ninja = { 
  yell: function(n){ 
    return n > 0 ? ninja.yell(n-1) + "a" : "hiy"; 
  } 
}; 
console.log( ninja.yell(4) == "hiyaaaa", "A single object isn't too bad, either." ); 
 
var samurai = { yell: ninja.yell }; 
var ninja = null; 
 
try { 
  samurai.yell(4); 
} catch(e){ 
  console.log( false, "Uh, this isn't good! Where'd ninja.yell go?" ); 
}

var obj={name: "faizan", age:31}
    var obj2 = {name:obj.name};//obj2 pointing to the same memoray location of obj
    console.log("before making null obj::",obj2.name);
    console.log(obj==obj2,"::checking obj==obj2 while var obj2=obj");
    obj=null;  //obj became null
    console.log("after making null obj::",obj2.name);//now this will need to be null but is working why??