Today! We’re going to Continue TypeScript learning like you’re a smart 5-year-old who loves to build things and asks “why?” (which is the best thing ever).

& yes “why?” is my way of learning.

I've divided this into 20 Chapters. and will go one by one and each will be of 2 - 3 min. of read.
This is a Continuation, if you have not read Previous chapter - Chapter 2

This is Chapter ⓷ TS Mastering

🧩 Chapter 3: Managing Functions with Typescript!

(aka: “Telling your helpers what kind of stuff they’ll handle”)

🍳 Imagine this:

You have a kitchen robot 🧑‍🍳🤖

You tell it:

“Make me a sandwich with bread and cheese.”

But what if you accidentally say:

“Make me a sandwich with rocks and batteries”? 🪨🔋😨

In JavaScript, the robot might try to do it.
But in TypeScript, it says:

❌ “Hey! That’s not sandwich stuff!”

🛠️ Let’s build a function with types!

Without TypeScript (JavaScript):

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

add(5, "10"); // Uh oh! Output is "510"

With TypeScript:

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

add(5, 10);   // ✅ OK!
add(5, "10"); // ❌ Error! TS says: "I expected a number, not a string"

🧙‍♂️ Parts of a Typed Function:

function greet(name: string): string {
  return "Hello, " + name;
}

• name: string → input must be a string
• : string after the ) → function returns a string

💡 What if a function returns nothing?

That’s called void:

function logMessage(msg: string): void {
  console.log("Message:", msg);
}

Think of void like: “I’m just doing stuff, not giving anything back.”

🪄 Default and Optional Parameters

function greet(name: string = "friend") {
  console.log("Hi", name);
}

function greetAgain(name?: string) {
  console.log("Hello", name ?? "buddy");
}

• = means default
• ? means it’s optional

🧪 Example:

function multiply(a: number, b: number): number {
  return a * b;
}

const result = multiply(3, 4); // result is 12 ✅

Try changing 4 to "4" and see TypeScript stop you. 🛑

If you enjoyed this and want to master TypeScript and other technologies, follow the series and drop a like!🤝

I’m a passionate software developer sharing the cool things I discover, hoping they help you level up on your coding journey.

How i created my own State Management Library : Rethinking State Management in React — From a Dev, for Developers.