Prototype constructor in javascript

Question

What is the need or use of prototype in java script constructors?
what is the difference between the following two code samples?
/// 1 ///////////////
function cat(name) {
     this.name = name;
     this.talk = function() {
          alert( this.name + " say meeow!" )
this.changename=function(name){
this.name=name
and
/// 2 ///////////////
cat.prototype.changeName = function(name) {
     this.name = name;
Please explain the above code. I have not tried the sample code 1. I just ask you to explain. What is the need for concept of constructor in Java script, if I could call a normal function as a constructor with new operator and treat it as a normal function as such with out a new operator?

Answer 1

What is the similar between Java and Javascript?
The first 4 letters.
While you can usually get away with asking JS questions here because they often relate to web stuff, this type of question is a pure JS question and definitely doesn't belong here. Go find a Javascript forum.