Type Annotations In TypeScript

 Type annotations in TypeScript are a way of explicitly specifying the data type of a variable, function parameter, return value, or any other TypeScript entity. Type annotations help the TypeScript compiler catch type-related errors during development, ensuring more robust and maintainable code. Here's an overview of type annotations in TypeScript:

1. Basic Type Annotations:

Variables:

let num: number = 10;

let str: string = "Hello";

let bool: boolean = true;

Function Parameters:

function greet(name: string): void {

    console.log("Hello, " + name);

}

Return Types:

function add(a: number, b: number): number {

    return a + b;

}

2. Arrays and Objects:

Arrays:

let numbers: number[] = [1, 2, 3];

let names: string[] = ["John", "Jane", "Doe"];

Objects:

let person: { name: string, age: number } = { name: "John", age: 30 };

3. Interfaces:

interface Person {

    name: string;

    age: number;

}

let john: Person = { name: "John", age: 30 };

4. Union Types:

let value: string | number;

value = "Hello";

value = 10;

5. Type Aliases:

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

function getDistance(point1: Point, point2: Point): number {

    // Calculate distance

}

let origin: Point = { x: 0, y: 0 };

6. Function Types:

type MathOperation = (a: number, b: number) => number;

let add: MathOperation = function(x, y) {

    return x + y;

};

7. Type Assertion:

let value: any = "Hello";

let length: number = (value as string).length;

8. Built-in Types:

let date: Date = new Date();

let regex: RegExp = /[a-zA-Z]+/;

9. Void and Never:

function logMessage(message: string): void {

    console.log(message);

}

function throwError(message: string): never {

    throw new Error(message);

}

These are some examples of type annotations in TypeScript. By using type annotations effectively, developers can improve the clarity, correctness, and maintainability of their code.