Challenge 1 — Solution

Task: Using the module pattern (IIFE returning an object), build a
TodoModule with private state (an array) and a public interface of
addTodo(text) and getAll(). Add 3 todos and log the result of
getAll(), then confirm TodoModule.todos is undefined.

const TodoModule = (function () {
    let todos = [];

    return {
        addTodo(text) {
            todos.push(text);
        },
        getAll() {
            return todos;
        }
    };
})();

TodoModule.addTodo("Buy milk");
TodoModule.addTodo("Walk the dog");
TodoModule.addTodo("Write JS notes");

console.log(TodoModule.getAll());
console.log(TodoModule.todos);


Expected output:

["Buy milk", "Walk the dog", "Write JS notes"]
undefined


Notes:
- The IIFE — (function () { ... })() — runs immediately the moment
  TodoModule is declared, and only the returned object (with
  addTodo and getAll) becomes TodoModule's actual value.
- todos lives entirely inside the closure created by the IIFE —
  there is no way to reach it except through addTodo/getAll, which
  is exactly why TodoModule.todos is undefined.
- getAll() returns the real array, not a copy — calling addTodo
  again later would still affect what a previously-stored reference
  to getAll()'s result shows, since arrays are reference types
  (Intermediate Chapter 6).