What are Arrow/lambda functions in TypeScript ?

Arrow functions in TypeScript (also known as lambda functions) are concise and lightweight function expressions using the => syntax.

• Provide a shorter syntax for defining functions.
• Automatically bind the context of their surrounding scope.
• It is commonly used for callbacks, array methods, and simple one-liner functions.

Syntax:

(param1, param2, ..., paramN) => expression;  //Arrow function having multiple parameters
() => expressions; //Arrow function with no parameters

const greet = (name: string): string => `Hello, ${name}!`;

console.log(greet("Alice"));

Output:

Hello, Alice!

More Example of Arrow function in TypeScript

Arrow Function in a Class

class Calculator {
    add = (a: number, b: number): number => a + b;
}

const calc = new Calculator();
console.log(calc.add(5, 3));

• The Calculator class includes an add method defined as an arrow function, which takes two numbers and returns their sum.
• Using an arrow function ensures that the method inherits the this context from its enclosing class.

Output:

8

Arrow Function with Array Methods

const numbers = [1, 2, 3, 4, 5];
const squared = numbers.map(n => n * n);
console.log(squared);

• An arrow function is used within the map method to square each number in the numbers array.
• This concise syntax enhances readability when performing operations on array elements.

Output: 

[1, 4, 9, 16, 25]

Arrow Function as a Callback

setTimeout(() => {
    console.log("This message is displayed after 1 second.");
}, 1000);

• An arrow function is passed as a callback to setTimeout, which logs a message after a 1-second delay.
• Arrow functions are ideal for inline callbacks due to their concise syntax and lexical this binding.

Output:

This message is displayed after 1 second.

Best Practices for Using Arrow Functions in TypeScript

• Use Arrow Functions for Short Callbacks: Arrow functions are ideal for short and concise callback functions in methods like map, filter, and reduce.
• Avoid Arrow Functions for Methods in Classes: Use regular functions for class methods that require dynamic this binding, as arrow functions inherit the this context.
• Return Object Literals Correctly: Wrap object literals in parentheses when returning them in single-line arrow functions to avoid syntax errors.
• Use Arrow Functions to Maintain this Context: Arrow functions are useful in scenarios where you want to preserve the this context in event handlers or asynchronous code.