Lesson 4: Working with Functions

Defining Functions

function greet(name: string): void {
  console.log("Hello, " + name);
}

This function accepts a string and does not return a value, so its return type is void.

Return Types

function add(a: number, b: number): number {
  return a + b;
}

Optional Parameters

function welcome(name: string, title?: string): void {
  if (title) {
    console.log("Welcome, " + title + " " + name);
  } else {
    console.log("Welcome, " + name);
  }
}

Default Parameters

function greetVisitor(name: string = "Guest"): void {
  console.log("Hello, " + name);
}

Arrow Functions

const square = (num: number): number => {
  return num * num;
};

Arrow functions provide a shorter modern syntax and are very common in JavaScript and TypeScript projects.

Summary

Functions become much safer in TypeScript because parameters and return values can be clearly typed. This makes larger programs easier to maintain and debug.