Javascript Module Pattern

module.js

const MyCoolModule = (() => {
  let
    privateState = {},
    privateVariable = 'private',
    bothPrivateAndPublicVariable = 'private and public',
  
  init = () => {
    // do some initialization stuff
    console.log('Initialized MyCoolModule!');
  },
  
  privateFunctionA = (k, v) => {
    privateState[k] = v;
    console.log('private state', privateState);
  },
  
  privateFunctionB = (arg) => {
    // do something
  };

  init();

  return {
    publicVariable: 'public',
    publicFunction: privateFunctionA, // private function made public
    bothPrivateAndPublicVariable,
  };
})();

//=> 'Initialized MyCoolModule!' in console on page load

MyCoolModule.publicVariable; //=> 'public'
MyCoolModule.publicFunction('a', 1); //=> 'private state {a: 1}' in console
MyCoolModule.publicFunction('b', 2); //=> 'private state {a: 1, b: 2}' in console
MyCoolModule.bothPrivateAndPublicVariable; //=> 'private and public'