IIFE.js

var articlesService = (function () {
  var articles = [1,2,3];
   
  function getArticles() {
    return articles;
  }
  
  function addArticle(article) {
    articles.push(article);
  }
  
  return {
    getArticles: getArticles,
    addArticle: addArticle
  };
  
}());