A function is a reusable block of code with a name. You write it once, then call it as many times as you need.

Declaring and calling a function

function direBonjour(prenom) {
  console.log("Bonjour " + prenom);
}
direBonjour("Marie");

Here, prenom is a parameter: a piece of information the function receives in order to do its job.

Returning a value

A function can send back a result with the return keyword:

• The result can be stored in a variable.
• Once return runs, the function stops.

function addition(a, b) {
  return a + b;
}
let total = addition(3, 4); // 7

Functions keep code organised and avoid repetition: a change in one place takes effect everywhere the function is called.

Key takeaway: a function bundles reusable code. It takes parameters and can send back a result with return.