Lesson 14 — Modules pattern

Hide the inside, share the outside

A good module exposes a small API (the functions others may call) and hides its internals. A closure does this: variables declared inside a function stay private, but functions returned from it can still use them.

const calc = (() => { let s = 0; return { add: (x) => { s += x; } }; })();

Nobody outside can touch s directly.

Why it matters: private state cannot be broken by accident from another file.