Classes and Instances

Classes and Instances

In this lesson — part of Objects and Classes — you'll learn classes and instances in JavaScript and why it matters in real work.

Why it matters

Classes bundle data and behavior together — the core of object-oriented design.

Key ideas

• Classes and instances
• Fields and methods
• Constructors
• Encapsulation

In practice

Here's how it looks in idiomatic JavaScript:

class Counter {
  count = 0;                 // class field
  increment() {
    return ++this.count;
  }
}
const c = new Counter();
console.log(c.increment(), c.increment()); // 1 2

JavaScript note: class is syntactic sugar over JavaScript's prototype-based inheritance, and methods you define live on the prototype shared by all instances.

Try it yourself

Exercise: In JavaScript, write a Bank Account class with deposit and withdraw methods.

Recap

You now understand classes and instances and can apply it in JavaScript. Mark this lesson complete and continue to the next one.