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Getters and Setters

Prototype vs Static, Getters and Setters

Properties assigned to this in the constructor belong to each instance. Methods and accessors in the class body are shared on Animal.prototype. static members live on the class itself; instances reach them through this.constructor.

Instance, prototype and static membersJavaScriptLive
class Animal {
  static count = 0;                                          // static: lives on Animal itself
  constructor(name) { this.name = name; Animal.count++; }    // own property of each instance
  eat() { return `${this.name} eats.`; }                     // shared, on Animal.prototype
  whoami() { return `${this.constructor.name}: ${this.eat()}`; }
  get intro() { return `This is ${this.name}.`; }             // read like a property
  set rename(n) { this.name = n; }                            // runs on assignment
  static comment() { return 'Animals are cute.'; }
}
const b = new Animal('Brownie');
b.rename = 'Greenie';
console.log(b.intro, b.whoami(), Animal.comment(), Animal.count);
console.log(Object.keys(b), Object.hasOwn(Animal.prototype, 'eat'), typeof Animal);

A class is still a function, but its body is strict, its methods are non-enumerable, and calling it without new throws. A method passed as a callback loses this; bind it or wrap it in an arrow function.