Difference between Object.create & new keyword in javaScript

Question

why output is coming on one case and not on the other? both of them have a variable inside their proto , yet I am getting undefined in one case.

Answer 1

When you type p.constructor.prototype.a the JavaScript checks for property constructor in the object itself but it does not have it. When that occurs, it goes over the prototype chain via __proto__. The problem here is that the object p and it's prototype(s) does not have property constructor. This is caused by use of Object.create(). Difference between it and new is already described in Understanding the difference between Object.create() and new SomeFunction() as @adiga commented under you post :)

Answer 2

It is very simple.

new a is Object.create(a.prototype)

while Object.create(a) is different than Object.create(a.prototype). new runs constructor code while object does not run constructor.

See following example:

function a(){
    this.b = 'xyz';
};

a.prototype.c = 'test';
var x = new a();
var y = Object.create(a);

//Using New Keyword
console.log(x); //Output is object
console.log(x.b); //Output is xyz.
console.log(x.c); //Output is test.

//Using Object.create()
console.log(y); //Output is function
console.log(y.b); //Output is undefined
console.log(y.c); //Output is undefined