Callbacks.

Seventh class. After the ordinary function declaration from Foundations, we learn a shorter syntax: the arrow function.

Arrow function: const double = (n) => n * 2; Short and common in JS.

In this lesson, store it in const and call it directly. Passing it as a callback argument comes next:

const addFee = (n) => n + 5; console.log(addFee(0));

Common mistake: writing => without parentheses when there are multiple parameters; or (n) => { n * 2 } without return.