Class.prototype.method vs this.prototype.method

Question

I've always seen examples of Class.prototype.method, but never instances of this.prototype.method. For example:

function Class() {     this.prototype.method = function() {         alert("is this allowed?");     }; } 

vs

function Class() {} Class.prototype.method = function() {     alert("traditional example"); }; 

1. Does this.prototype exist?
2. Is it the same as Class.prototype?
3. What about inheritance?

Answer 1

1. Does this.prototype exist?

   No. But, this.constructor.prototype should.

2. Is it the same as Class(.constructor).prototype?

   It will generally have the same value (so long as this.constructor === Class), but not the same intent.

3. What about inheritance?

   Each new Class instance will inherit from Class.prototype. So, a prototype object is good for defining shared values accessible to all instances. Then, the constructor just has to setup state that's unique to each instance.

   But, attempting to mix the 2 and set a prototype property within the constructor has a few problems, including a chicken-or-egg conflict as the method won't exist until the first instance is created:

   function Class() {     this.constructor.prototype.method = function () {}; }  console.log(typeof Class.prototype.method); // "undefined"  var a = new Class();  console.log(typeof Class.prototype.method); // "function" 

   And defeats some of the benefit of having the prototype as the method is being recreated with each additional instance:

   var method = a.method;  console.log(a.method === method); // true  var b = new Class();  console.log(a.method === method); // false