Using Types.md

Using Types

Introduction

The use of types is a fundamental aspect of the language, and it's one of the key features that differentiates TypeScript from JavaScript.

Table of Contents

• 1. Type Annotations:
• 2. Function Parameters and Return Types:
• 3. Interfaces:
• 4. Arrays and Generics:
• 5. Union and Intersection Types:
• 6. Type Aliases:
• 7. Enums:
• 8. Classes:
• 9. Type Assertion:
• 10. Declaration Files (.d.ts):

1. Type Annotations:

• You can explicitly declare the type of a variable using type annotations. For example:

  let name: string = "John";
  let age: number = 25;

2. Function Parameters and Return Types:

• Specify the types of function parameters and return values:

  function add(x: number, y: number): number {
      return x + y;
  }

3. Interfaces:

• Use interfaces to define the shape of objects:

  interface Person {
      name: string;
      age: number;
  }
  
  let person: Person = {
      name: "Alice",
      age: 30
  };

4. Arrays and Generics:

• Use generics to create reusable components with dynamic types:

  let numbers: Array<number> = [1, 2, 3, 4];

5. Union and Intersection Types:

• Combine types using unions or intersections:

  type Status = "success" | "error";
  type Result = { value: number } & { message: string };

6. Type Aliases:

• Create your own custom types with type aliases:

  type Point = {
      x: number;
      y: number;
  };

7. Enums:

• Use enums to define a set of named constants:

  enum Color {
      Red,
      Green,
      Blue
  }
  
  let myColor: Color = Color.Green;

8. Classes:

• Define classes with typed properties and methods:

  class Dog {
      name: string;
  
      constructor(name: string) {
          this.name = name;
      }
  
      bark(): void {
          console.log("Woof!");
      }
  }
  
  let myDog: Dog = new Dog("Buddy");

9. Type Assertion:

• Use type assertion to explicitly specify a type when TypeScript cannot infer it:

  let myVariable: any = "Hello, TypeScript!";
  let stringLength: number = (myVariable as string).length;

10. Declaration Files (.d.ts):

• Use declaration files to provide type information for external libraries or JavaScript code:

  // example.d.ts
  declare module "example-library" {
      function myFunction(value: string): number;
  }

These are just a few examples of how you can use types in TypeScript. Types provide a powerful way to catch errors early in the development process, improve code documentation, and enable better tooling support in modern development environments.