How to Declare a Class in Typescript?

To declare a class in TypeScript, we make use of the class keyword followed by the class name.

class Student {}

This creates an empty class.

Adding fields in a class

Fields are properties of a class that can be used to assign values. Let’s declare two fields name and age for our Student class.

class Student {
  name: string;
  age: number;
}

Here, we have declared the type of name to be a string and the age to be a number.

Let’s create an object of class Student and assign some values. To create an object we will use the new keyword.

let student = new Student();

This will create an object student of class Student. Since we have declared two properties, let’s assign them some values.

student.name = "Bob";
student.age = 12;

console.log(student); // Student {name: 'Bob', age: 12}

If we try to assign a different type to any of the class fields, the typeScript will complain about it.

student.age = "Twelve"; // Type 'string' is not assignable to type 'number'.

How to use constructor() in typescript?

A constructor method in Typescript is used to initialize an object. TypeScript uses the constructor keyword to declare a constructor within a class. The properties of the class can be initialized within the constructor method.

class Student {
  name: string;
  age: number;

  constructor(name: string, age: number) {
    this.name = name;
    this.age = age;
  }
}

let student = new Student("Bob", 12);

console.log(student); // Student {name: 'Bob', age: 12}

The constructor method takes two arguments and using the this keyword we assign the name and age properties. The values for these properties get passed when creating an object new Student('Ron', 1)