What are getters and setters in JavaScript?

Getters and setters are special methods that execute code when a property is read or written — they look like properties but behave like functions.

const user = {
  firstName: 'John',
  lastName: 'Doe',

  get fullName() {
    return `${this.firstName} ${this.lastName}`; // computed on read
  },

  set fullName(val) {
    [this.firstName, this.lastName] = val.split(' '); // validated on write
  }
};

console.log(user.fullName); // 'John Doe' — runs getter
user.fullName = 'Jane Smith'; // runs setter
console.log(user.firstName); // 'Jane'

// In a class
class Temperature {
  constructor(celsius) { this._c = celsius; }

  get fahrenheit() { return this._c * 9/5 + 32; }
  set fahrenheit(f) { this._c = (f - 32) * 5/9; }
}

const t = new Temperature(0);
console.log(t.fahrenheit); // 32
t.fahrenheit = 212;
console.log(t._c);         // 100