Getting Started with TypeScript

TypeScript is an open-source programming language developed by Microsoft that extends JavaScript by adding optional static typing to the language. It aims to make JavaScript development more scalable and maintainable, especially for large-scale projects. TypeScript code is transpiled into JavaScript code, making it compatible with all modern browsers and JavaScript frameworks.

TypeScript Basics

TypeScript any Type:

The any type in TypeScript allows variables to hold values of any data type. It is often used when the type of a variable is not known during development or when interfacing with JavaScript libraries that have dynamic typing.

Syntax:

let value: any;

TypeScript union type:

Union types allow a variable to hold values of multiple types. For example, number | string denotes a variable that can be either a number or a string.

Syntax:

let Variable_name: data_type1 | data_type2

Example:

function display(value: number | string) {
    if (typeof value === "number") {
        console.log("The value is a number:", value);
    } else {
        console.log("The value is a string:", value.toUpperCase());
    }
}
display(22);          // Output: The value is a number: 22
display("gfg"); // Output: The value is a string: GFG

Type aliases:

Type aliases allow developers to create custom names for existing types, making complex types more readable and easier to maintain.

Syntax:

type type_name = create_your_type;

Example:

type Point = { x: number; y: number };
const point: Point = { x: 10, y: 20 };
console.log(point); // Output: { x: 10, y: 20 }

interface:

Interfaces define the structure of an object in TypeScript. They can include properties, methods, and optional members. Interfaces are commonly used for defining contracts within the codebase

Syntax:

interface Name_of_interface{
key : value, 
key : value
}

Example:

interface Person {
    name: string;
    age: number;
}
function greet(person: Person): string {
    return `Hello, ${person.name}!`;
}
const user: Person = { name: "GFG", age: 22 };
console.log(greet(user)); // Output: Hello, GFG!

Enums:

Enums (short for enumerations) allow developers to define a set of named constants. Enums are useful for representing a fixed set of values within the codebase.

Syntax:

enum nafe_of_enum{
value1,
value2, 
.
.
.
value_n
}

Example:

enum DayOfWeek {
    Sunday,
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday
}
function getDayName(day: DayOfWeek): string {
    return DayOfWeek[day];
}
console.log(getDayName(DayOfWeek.Monday)); // Output: Monday

Example 1: This example shows the use of Type Guards with Arrays.

Javascript

// Define a type guard function
function isNumberArray(arr: any[]):
    arr is number[] {
    return arr.every(item => typeof item === "number");
}

// Use the type guard in a conditional statement
function sumOrJoin(arr: number[] |
    string[]): number | string {
    if (isNumberArray(arr)) {
        return arr.reduce((acc, curr) =>
            acc + curr, 0);
    } else {
        return arr.join(", ");
    }
}

console.log(sumOrJoin([1, 2, 3]));
console.log(sumOrJoin(["hello", "world"])); 

Output:

6
hello, world

Example 2: This example shows the use of Type Guards with Objects.

Javascript

// Define a type guard function
function isPerson(obj: any): obj is
    { name: string; age: number } {
    return typeof obj === "object" &&
        "name" in obj && "age" in obj;
}

// Use the type guard in a conditional statement
function greet(obj: {
    name: string;
    age: number
} | string): string {
    if (isPerson(obj)) {
        return `Hello, ${obj.name}!`;
    } else {
        return `Hello, ${obj}!`;
    }
}

console.log(greet({ name: "Gfg", age: 22 }));
console.log(greet("world"));                   

Output:

Hello, Gfg!
Hello, world!

Steps to Run the Code

• Step1: Install Node.js from official website.
• Step2: Install TypeScript globally by running npm install -g typescript in your terminal.
• Step3: Copy the code examples into separate TypeScript files (.ts extension).
• Step4: Compile the TypeScript files into JavaScript using the TypeScript compiler (tsc) by running tsc filename.ts.
• Step5: Run the generated JavaScript files using Node.js or include them in an HTML file for browser execution.

Advantages of Using TypeScript

• Static Typing: TypeScript provides type safety, catching errors at compile time and improving code quality.
• Enhanced Tooling: TypeScript offers better IDE support with features like code completion, refactoring tools and inline documentation.
• Code Maintainability: By enforcing type safety and providing clearer interfaces, TypeScript enhances code maintainability and readability.

How to Use TypeScript in a Project?

• Create a new TypeScript file with the .ts extension.
• Write your TypeScript code as usual.
• TypeScript allows you to gradually adopt static typing by adding type annotations where needed.
• Compile the TypeScript code into JavaScript using the TypeScript compiler (tsc).
• Include the generated JavaScript files in your project as you would with any other JavaScript files.