Scope.

Tenth class. A variable created inside a function lives only there — that is scope. Outside, you cannot see it.

So functions take parameters and return with return, instead of leaning on “global” names everywhere. Code stays clearer and safer.

Mini example:

function label(n) { const text = "left"; return text; } console.log(label(1));

Common mistake: expecting to use an inner const outside the function — you get ReferenceError.