title: how to do `var self = this` inside es6 class?
body: <p>I am running the below code in nodejs</p>
  
  <pre><code>this.x = 'global x';
  class Point {
      constructor(x) {
          this.x = x;
      }
      toString() {
          return this.x;
      }
  }
  var obj = new Point(1);
  obj.toString();// 1 as expected
  var a = obj.toString;// Here I can do something like var a = obj.toString.bind(obj); to get rid of the situation. But I am curious to know how can we write `var self = this`;
  a();// TypeError: Cannot read property 'x' of undefined
  </code></pre>
  
  <p><code>a();</code> throws the error.<br>
  How can we do like <code>var self = this;</code> as we used to do in <code>es5</code> to prevent such a situation?</p>