Class basics

Learn to define classes in TypeScript.

What is a class?

A class is a blueprint for objects that share structure and behavior. Fields are variables defined inside the class; under strict mode they must have an initial value. You create a new instance with new.

class Person {
  name: string = "";
  age: number = 0;
}
const p = new Person();
p.name = "Ada";
console.log(p.name);

Fields

Class fields are defined with just a name and a type, without let or const. Under strict mode an initial value is required. After creating an instance, you access fields with a dot and assign values.

class Point {
  x: number = 0;
  y: number = 0;
}
const pt = new Point();
pt.x = 3;
pt.y = 4;

Exercise Write a Car class

Define a Car class with make: string = "" and model: string = "" fields. Create a new Car instance, set make to "Toyota" and model to "Corolla", and print the make field.

Show example solution

class Car {
  make: string = "";
  model: string = "";
}

const car = new Car();
car.make = "Toyota";
car.model = "Corolla";
console.log(car.make);

Test yourself

Which keyword is used to create an object from a class?
- create
- make
- instance
- new
Show answer

new — The new keyword creates a new instance from a class. create, make, and instance are not valid TypeScript keywords.

Complete the class definition

____ Dog {
  name: string = "";
}

Show answer

class Dog {
  name: string = "";
}

Class basic parts

class

Class definition keyword
new Person()

Create a new instance
name: string

Class field
p.name

Field access

Next lesson: Constructor and fields

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