function Article() {
  this.tags = ['js', 'css'];
}

Article.prototype.printTagsList = function() {
  console.log( this.tags.join(', '));
};

var article = new Article();

function BlogPost() {}

BlogPost.prototype = article;

var blog = new BlogPost();

function StaticPage() {
  Article.call(this);
}

var page = new StaticPage();

blog.printTagsList();
page.printTagsList();