Private prototype functions and provate memebers in native javascript.

privicyInJavascriptClasses.js

// Closure is necessary to get rid of 'strict mode' as `args.callee.caller` cannot be used in 'strict mode'
(function (scope) {

  // LeClass declaration
  // ===================
  scope.LeClass = function () {
      
    // Private members declared in private namespace `prv`
    var prv = {
      trala: 'you touch my tralala...',
      ding: 'my ding ding dong...'
    };

    // `getter` for private members. This function needs to be declared here instead of in prototype
    // in order to get access to `prv`
    this._get = function(variableName) {
      checkAccessibility.apply(this, [arguments]);
      return prv[variableName]
    }

    // Private methods can also be called from the constructer
    this.privateMethodTralala();
  };

  LeClass.prototype.publicMethod = function (item) {
    // Private methods of class `LeClass` are only accessible from LeClass' public methods
    this.privateMethodTralala();
  };

  LeClass.prototype.privateMethodTralala = function (item) {
    checkAccessibility.apply(this, [arguments]);

    console.log(this._get('trala') + ' ' +this._get('ding'));
  };

  function checkAccessibility(args) {
    var prototyp = Object.getPrototypeOf(this);
    if (args.callee.caller == prototyp.constructor) {
      return;
    }

    for (var key in prototyp) {
      if (prototyp.hasOwnProperty(key)) {
        if (prototyp[key] == args.callee.caller) {
          return;
        }
      }
    }
    throw 'Access violation, this function is private';
  }
    
  return;

}(window));

// Show time
// ---------
var myObject = new LeClass();

// This will succeed
myObject.publicMethod();

// Those will fail
try{
  myObject.privateMethodTralala();
}
catch(e){
  console.error(e);
}

console.log(myObject._get('trala'));

// Expected output
// ---------------
//     you touch my tralala... my ding ding dong... 
//     you touch my tralala... my ding ding dong... 
//     Access violation, this function is private 
//     Uncaught Access violation, this function is private