declaration of member variables in ES6 classes
<p>I've seen member variables in ES6 declared like this</p>

<pre><code>export class MyClass
{
   x = null;

   constructor()  {
      this.x = 1;
   }

   write() {
      console.log(this.x);
   }
}
</code></pre>

<p>and babel seem to transpile it fine.</p>

<p>Is this a valid way to declare member variables?</p>