Classes and Types

This lesson covers the basics of writing a class in TypeScript. It's for anyone searching "TypeScript class usage."

The big difference from JavaScript is that a TypeScript class can have typed properties. The constructor receives initial values, and each property is declared with a type annotation.

The example defines class Animal with a name: string property and a speak() method that returns a sound.

A common early mistake is forgetting to declare a property in the class body. In a TypeScript class, it's not enough to just type the constructor's parameter — you also need to declare the property in the class body itself, like name: string; (though adding public to the constructor's parameter lets you skip this).

In real projects, classes are used to represent data that bundles state and behavior together — a game character, or a "product" or "user" in a business app.

📖 Reference code

class Animal {
  name: string;
  constructor(name: string) {
    this.name = name;
  }
  speak(): string {
    return `${this.name} is barking.`;
  }
}

const dog = new Animal("Rex");
console.log(dog.speak());

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run TypeScript directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).