title: Pass 'this' to a class variable inside constructor
body: <p>I am interested, how to pass <code>this</code> to a class variable inside a constructor of a parent, so I could use parents methods and access other variables of the parent and call their methods?
  <br>
  Here is my parent class:<br><br></p>
  
  <pre><code>var async = require('async');
  var Rater = require('./rater')
  var Similars = require('./similars')
  var Suggestions = require('./suggestions');
  
  module.exports = class Engine {
      constructor() {
          this.likes = new Rater(this,'likes');
          this.dislikes = new Rater(this,'dislikes');
          this.similars = new Similars(this);
          this.suggestions = new Suggestions(this);
      }
  </code></pre>
  
  <p>And here is the example of usage and where is get the following error:<br></p>
  
  <pre><code>Cannot read property 'engine' of undefined
  at --\\classes\rater.js:89:19
  </code></pre>
  
  <p><br></p>
  
  <pre><code>module.exports = class Rater {
    constructor(engine,kind) {
      this.type = kind;
      this.engine = engine;
      if(kind == 'likes') //database schemes
        this.db = Likes_db;
      else if(kind == 'dislikes')
        this.db = Dislikes_db;
      else if(kind == 'similars')
        this.db = Similars_db;
      else if(kind == 'suggestions')
        this.db = Suggestions_db;
    }
    //..
    //other methods
    //..
    remove(user,item,done) {
        this.db.remove({user: user,item: item},(err) =&gt; {
          if(err)
            return done(err);
          async.series([
            function(done) {
                this.engine.similars.update(user,done); //error-cant enter the method
            },
            function(done) {
              this.engine.suggestions.update(user,done);
            }
          ],function(done) {
  
          });
      });
    }
  }
  </code></pre>