Understanding Prototype in JavaScript

The Prototype Chain

When you access a property on an object, JavaScript first looks at the object itself; if not found, it looks up the prototype chain until it finds the property or reaches null.

let arr = [1, 2, 3];
console.log(arr.__proto__ === Array.prototype); // true

Adding Methods via Prototype

Array.prototype.first = function() {
    return this[0];
};
console.log([10, 20, 30].first()); // 10

Object.create()

let animal = { eats: true };
let rabbit = Object.create(animal);
console.log(rabbit.eats); // true, inherited via prototype