Getters and Setters in JavaScript

Sometimes you want something that looks like a property but is actually calculated. For that, classes have getters, written with the keyword get:

JavaScript

class Person {
  constructor(firstName, lastName, birthYear) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.birthYear = birthYear;
  }

  get fullName() {
    return `${this.firstName} ${this.lastName}`;
  }

  get age() {
    return 2026 - this.birthYear;
  }
}

const person = new Person("Emma", "Garcia", 2001);
console.log(person.fullName);
console.log(person.age);

person.firstName = "Chloe";
console.log(person.fullName);

It prints

Emma Garcia
25
Chloe Garcia

Notice there are no parentheses: you write person.fullName, not person.fullName(). It's used just like a normal property, but it's worked out fresh every time you read it. So when the first name changes, fullName automatically updates.

A setter, written with set, runs when you assign to a property. It's perfect for validation: checking that a value makes sense before accepting it.

JavaScript

class Thermostat {
  constructor() {
    this._temperature = 22;
  }

  get temperature() {
    return this._temperature;
  }

  set temperature(value) {
    if (value < 10 || value > 30) {
      console.log(`❌ ${value}°C is out of range! Keeping ${this._temperature}°C.`);
      return;
    }
    this._temperature = value;
    console.log(`🌡️ Temperature set to ${value}°C`);
  }
}

const thermostat = new Thermostat();
thermostat.temperature = 25;
thermostat.temperature = 99;
console.log(thermostat.temperature);

It prints

🌡️ Temperature set to 25°C
❌ 99°C is out of range! Keeping 25°C.
25

(The underscore in _temperature is a common convention meaning "this is an internal property; please don't touch it directly." But it's only a polite request. Anyone can still change it. For real privacy, keep reading.)

Reading is step one