title: Why event or this in constructor properties wont work
body: <p>I have video stream code with blobs and MediaRecorder. And I'm trying to rewrite my old code on es6. </p>
  
  <p>If I call the method without brackets then <code>this.property</code> does not work (returns <code>undefined</code>). If I call the method with brackets, "e" stops working.</p>
  
  <pre><code>class testClass {
    constructor() {
      this.blobdata = [];
    }
  
    startRecording() {
      this.mediaRecorder.ondataavailable = this.handleDataAvailable;
      // this.handleDataAvailable if try like that - 'this.blobdata' returns undefined in handleDataAvailable(e)
     // this.handleDataAvailable() if try like that - e.data return undefined...
    }
  
    handleDataAvailable(e) {
       // there is error (this.blobdata returns undefined) 
       if (e.data &amp;&amp; e.data.size &gt; 0) this.blobdata .push(e.data)
    }
  
  }
  
  let sc1 = new testClass();
  let sc2 = new testClass();
  </code></pre>