How to hide a utility method?

Question

JavaScript

Hello! How to hide a utility method? When adding ennumerable: false to the method descriptor, but in this case I cannot use it in other methods of the object, it throws the error "TypeError: this._load is not a function". Who will advise what?

"use strict"
var fs = require('fs');


function Settings(pathToJson) {
  typeof pathToJson === "string" ? this.reload(pathToJson) : this.reload('./settings.json');
  Object.defineProperties(this, {
    _load: {enumerable: false},
    settings: {enumerable: false}
  });
  Object.freeze(this);
}

Settings.prototype = {

  reload: function(path){
    this.settings = fs.readFileSync(path, 'utf-8');
    this.settings = this.settings.replace(/\/\/.*/g, '');
    this.settings = JSON.parse(this.settings);
  },

  _load: function(){
    fs.writeFileSync('settings.json', JSON.stringify(this.settings, false, '\t'));
  },
  
  get include(){
    return this.settings.include;  
  },

  set include(arg){
    if (arg instanceof Array) { // В том случае если передают массив
      var _ = this;
      arg.forEach(function(c, i){
        
        // Если в массиве находятся не строки выкидывает ошибку!
        if (!(typeof c === 'string')) throw new Error('Path not readable!');
        
        // Если путь найден в инклудах или ексклудах путь не подключается!
        if(~_.include.indexOf(c) || ~_.exclude.indexOf(c)) return;
        
        // Создание инклуда и подключение путей
        _.include = [];
        _.include.push(c);
        console.log('includig ' + c);							
      });
      this._load();   // 	<== Здесь выскакивает ошибка
    }

    else if (typeof arg === 'string'){ // В том случае если передают один путь
      if(~this.include.indexOf(arg) || ~_.exclude.indexOf(arg))  return;
      this.include = [];	// Создание инклуда и подключение путей
      this.include.push(arg);
      this._load();	//	<== Здесь выскакивает ошибка	
    }

    else throw new Error('Path not readable!');
  },

  get exclude(){
    return this.settings.exclude; 
  }
}

Answer 1

Use Node.js 6, it already has classes and arrow functions. The code will become much more compact and beautiful.
Regarding service methods: if you mean private methods, then there is no special need for this. But if you still really need it, this is done through a Symbol, WeakMap or a closure. Examples can be easily googled. There is also an option with decorators https://github.com/elado/class-private-method-decorator
But for it you need to include Babel in the project.
PS If you need a clean syntax, you can use TypeScript. Example from documentation:

class Animal {
    private name: string;
    constructor(theName: string) { this.name = theName; }
}

new Animal("Cat").name; // Error: 'name' is private;

Answer 2

And I keep reading a book on ES5 and thought that it is possible to use such constructions of private methods using descriptors. Thanks for the directions!