prototype-classes.js

// 1. constructor
function Animal(name) {
  this.name = name;
  this.speed = 0;
}

// 2. methods in prototype
Animal.prototype.run = function(speed) {
  this.speed += speed;
  console.log(`${this.name} runnig, speed is ${this.speed}`);
};

Animal.prototype.stop = function() {
  this.speed = 0;
  console.log(`${this.name} стоит`);
};

var animal = new Animal('Banny');

console.log( animal.speed ); // 0, from __proto__
animal.run(5); // Banny runnig, speed is 5
animal.run(5); // Banny runnig, speed is 10
animal.stop(); // Banny runnig