How does prototypal inheritance work in JavaScript?

Every JS object has an internal [[Prototype]] link. Property lookup walks up the chain until found or null.

const animal = { speak() { return '...'; } };
const dog = Object.create(animal); // dog's proto = animal
dog.name = 'Rex';
dog.speak(); // Found on chain → '...'

// ES6 class is sugar over this
class Dog extends Animal {
  speak() { return 'Woof!'; }
}