Methods
- TypeScript course
- Intermediate
- Lesson 3/89
- 4 min
Learn to add methods to classes.
Class methods
You define behavior by adding methods to a class. A method is written like a function in the class body and can access the instance's fields with this. It is called with a dot on the instance.
class Greeter {
name: string;
constructor(name: string) {
this.name = name;
}
greet(): string {
return "Merhaba, " + this.name;
}
}
const g = new Greeter("Ada");
console.log(g.greet());Calling methods
Methods are called with a dot on the instance: g.greet(). Inside the method, this refers to the instance it was called on. So when g.greet() is called, this.name is g's name field.
const g = new Greeter("Ada");
console.log(g.greet()); // "Merhaba, Ada"Practice Rectangle class and area method
Define a Rectangle class with width: number and height: number fields. Add a constructor that takes both parameters. Write an area(): number method that returns this.width * this.height. Create a new Rectangle(4, 5), call area(), and print the result.
Starter code
// Rectangle sınıfı tanımla (genişlik ve yükseklik)
// constructor ile her iki alanı al
// alan hesaplayan metot yaz (width * height)
// yeni Rectangle oluştur, çağır ve yazdırSample solution
class Rectangle {
width: number;
height: number;
constructor(width: number, height: number) {
this.width = width;
this.height = height;
}
area(): number {
return this.width * this.height;
}
}
const r = new Rectangle(4, 5);
console.log(r.area());Expected output
20
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does this refer to in a class method?
- The global object
- The class itself
- The parent class
- The instance that was called Correct answer
Explanation: this refers to the instance the method was called on. You access that instance's name field with this.name. It is not the class itself or the parent class.
2 Complete the method return
greet(): string {
return "Merhaba, " + ____;
}greet(): string {
return "Merhaba, " + this.name;
}Explanation: Inside a method you access the instance's name field with this.name. name is not defined, this gives the object itself, and Greeter.name is a static access (which does not exist).
3 Method parts
| Term | Meaning |
|---|---|
greet() |
Method definition |
this.name |
Instance field access |
g.greet() |
Method call |
: string |
Return type |