<aside> 💡

These are the building blocks of every JavaScript program. Master these and you can build anything.

</aside>

1. Functions

A function is a block of code you can run whenever you need it.

function welcome() {
  console.log("Salaam!");
}

welcome(); // Salaam!

Mental model: Function = a reusable instruction. Like telling someone how to make shaah once. They can make it anytime after that.

2. Parameters and Return

Parameters — give the function inputs

function welcome(name) {
  console.log("Salaam, " + name);
}

welcome("Ahmed");   // Salaam, Ahmed
welcome("Faadumo"); // Salaam, Faadumo

Multiple parameters

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

let result = add(3, 5);
console.log(result); // 8

console.log vs return

function double(n) {
  console.log(n * 2); // prints — but gives nothing back
}

function double(n) {
  return n * 2; // gives the value back — you can use it
}

let result = double(5);
console.log(result); // 10

Without return the function gives back undefined.

In practice

function calculateTotal(price, tip) {
  return price + tip;
}

let total = calculateTotal(200, 1);
console.log(total); // 220

Mental model: Parameters = ingredients you hand to the function. Return = the finished result it hands back.

3. Scope

Variables live where they are created.