Why cannot I use prototype in Object Literals in javascript?

Question

Well I am curios to learn about prototypes in javascript and found many articles however i am not able to understand why am i not able to use prototypes in Object literals in javascript. As we all know, everything is inherited from Object so in that case

function Dog() {
}

Dog.prototype = new Animal;
Dog.prototype.bark = function() {
    console.log("Woof! My name is " + this.name);
};

If I am able to use prototype in the function why am i not able to use prototype in the object literals for instance the below example

 var obj = {
            firstname: 'foo',
            lastname:'bar'
        }
        // this throws an error
        obj.prototype.getMethod = function () {
            console.log('this is a function');
        }

I have gone through all this question but it really doesnt answer the reason why cant use prototype in the object literals in javascript. Below are some of the references

refrence 1

refrence 2

refrence 3

Answer 1

First of all, the .prototype property belongs to function object. You cannot access it from a plain object instance. Basically the constructor-associated .prototype property will be used when constructing the internal [[prototype]] of an instance. Here you are having an instance, if you want to add the function to the prototype chain of it, then you have to modify it by

var obj = { firstname: 'foo', lastname:'bar' };
var pro = Object.getPrototypeOf(obj);
pro.getMethod = function () {
  console.log('this is a function');
};

As @bergi pointed out, there is a risk of adding the getMethod to all the instances if we follow the above approach. But in order to avoid that you could alternatively do,

var obj = { firstname: 'foo', lastname:'bar' };
Object.setPrototypeOf(obj, Object.create({getMethod : function(){
  console.log("Hello");
}}));

console.log(obj.getMethod()); //"Hello"