Prerequisite - understanding of proto

Simple Example

• The Object.create() method creates a new object, using an existing object as the prototype of the newly created object. Confusing? Let's understand it using an example

let src = {a: 1};

let result = Object.create(src);

console.log(result) // prints {}
console.log(result.__proto__ === src); // true
console.log(result.a); // prints 1

• So, by second log, We understand that if we make any changes in result.proto, it will change the src. Let's quickly check that

result.__proto__.a = 2;
console.log(src.a); // prints 2

• What if we want to attach directly some property to the created object? We can do so by passing a second argument as an object like below

let src = {a: 1};
let result2 = Object.create(src, {
  b : {
    value: 3
  }
});

console.log(result2) // prints {b: 3}
result2.hasOwnProperty('b') // prints true

• Notice, I didn't use {b:3} directly in the argument but I had to pass a property descriptor object

How is it used in case of function and prototype

• Let's take an example real quick. So, In below example, A completely new object was created with proto pointing to Base.Prototype and is assigned to Child.prototype.
• It can be powerfully used to achieve inheritance in JS

function Base() {
  this.a = 1;
}

Base.prototype.b = 2;

function Child() {}

Child.prototype = Object.create(Base.prototype);
console.log(Child.prototype.__proto__ === Base.prototype);

Child.prototype.__proto__.b = 3;
console.log(Base.prototype.b); // prints 3