Methods

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"

Exercise 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.

Show example 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());

Test yourself

What does this refer to in a class method?
- The global object
- The class itself
- The parent class
- The instance that was called
Show answer

The instance that was called — 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.

Complete the method return

greet(): string {
    return "Merhaba, " + ____;
  }

Show answer

greet(): string {
    return "Merhaba, " + this.name;
  }

Method parts

greet()

Method definition
this.name

Instance field access
g.greet()

Method call
: string

Return type

Next lesson: Static members

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