Module revealing pattern~ Design patterns ~

Module revealing pattern

The revealing module pattern is the one that I use the most in my daily job. Back in the days when we didn't have classes, this pattern was my primary tool for mimicking OOP.

The idea here is to create a scope and return an API. The scope encapsulates the logic and, the object that we return gives access to the public interface.

Imagine we have to write a music player:

function Player() {
  let trackId;
  function play(id) {
    trackId = id;
    console.log(`Track #${trackId} is started`);
  function stop() {
    console.log(`Track #${trackId} stopped`);
  function status() {
    console.log(`Processing track #${trackId}`);
  return {
const p = Player();; // Track #4 is started
p.status(); // Processing track #4
p.status(); // Processing track #4
p.stop(); // Track #4 stopped

We hide the variable trackId for the outside world. The functions play, stop, and status are our public API. It is similar to writing a class. The Player function acts as a constructor because we will get a new _instance_whenever we call it. With its own trackId and public methods.