JavaScript Academy · Lesson

The Module Pattern (IIFE)

Encapsulate code with immediately invoked functions.

Lesson 3 of 413 steps

The Module Pattern (IIFE) is a free JavaScript Academy lesson on CoddyKit. This is lesson 3 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the JavaScript Academy learning path, and your progress syncs across the web and the CoddyKit app. The JavaScript Academy course includes 4 lessons in total.

What the Module Pattern Solves

Before ES modules, the module pattern let you bundle related state and behavior while keeping internals private and exposing a clean public API. It is built on closures.

The IIFE

An IIFE (Immediately Invoked Function Expression) is a function that runs the moment it is defined. Wrapping in parentheses and calling it creates a private scope instantly.

const result = (function () {
  return 42;
})();
console.log(result); // 42

Why Run It Immediately

The IIFE gives you a one-time private scope without leaving a named function lying around. Everything inside is isolated from the global namespace.

(function () {
  const temp = "not global";
  console.log(temp);
})();
// temp is unreachable out here

Returning a Public API

The module pattern is an IIFE that returns an object. The object methods are closures over the private variables, forming the public interface.

const counter = (function () {
  let count = 0; // private
  return {
    inc: () => ++count,
    value: () => count
  };
})();
counter.inc();
console.log(counter.value()); // 1

Private vs Public

Anything declared inside but not returned stays private. Only what you put on the returned object is accessible.

const calc = (function () {
  const pi = 3.14159; // private constant
  return {
    area: (r) => pi * r * r
  };
})();
console.log(calc.area(2)); // 12.56636
console.log(calc.pi);      // undefined

Private Helpers

Helper functions can live inside the module, used by public methods but never exposed.

const validator = (function () {
  const clean = (s) => s.trim().toLowerCase(); // private
  return {
    isEmail: (s) => clean(s).includes("@")
  };
})();
console.log(validator.isEmail(" A@B.com ")); // true

The Revealing Module Pattern

A popular variant defines all functions privately, then returns an object that "reveals" references to the public ones. It keeps the public API list clear at the bottom.

const store = (function () {
  let items = [];
  function add(x) { items.push(x); }
  function count() { return items.length; }
  return { add, count }; // reveal
})();
store.add("a");
console.log(store.count()); // 1

Singletons

Because the IIFE runs once, a module is effectively a singleton: there is exactly one instance with one set of private state.

const config = (function () {
  let settings = { theme: "dark" };
  return {
    get: (k) => settings[k],
    set: (k, v) => { settings[k] = v; }
  };
})();
config.set("theme", "light");
console.log(config.get("theme")); // "light"

Passing in Dependencies

You can pass globals or other modules as IIFE arguments, making dependencies explicit and enabling safe minification.

const mathUtils = (function (M) {
  return { roundUp: (n) => M.ceil(n) };
})(Math);
console.log(mathUtils.roundUp(4.1)); // 5

Avoiding Global Pollution

The whole point is one global name (the module) instead of dozens of loose variables. This prevents naming collisions across scripts.

Relation to ES Modules

Today, import/export give true module scope at the language level, largely replacing this pattern. But understanding IIFE modules clarifies how privacy and encapsulation work, and you will still meet them in legacy code.

Quick Check

The module pattern and IIFEs.

Answer it in the interactive lesson

Recap

The module pattern uses an IIFE to create a private scope, returning an object whose methods are closures over hidden state. Internals stay private; only the returned members are public. Variants like the revealing module pattern clarify the API, and modules act as singletons. ES import/export now supersede the pattern but build on the same ideas.

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Frequently Asked Questions

Is the “The Module Pattern (IIFE)” lesson free?

Yes — any 3 lessons of the JavaScript Academy learning path, including “The Module Pattern (IIFE)”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The JavaScript Academy course includes 4 lessons in total.

What will I learn in “The Module Pattern (IIFE)”?

Encapsulate code with immediately invoked functions. You practise JavaScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start JavaScript Academy?

No prior experience is required. JavaScript Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

How long does the “The Module Pattern (IIFE)” lesson take?

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