title: Defining a Class in ES2015, what is the constructor method and why is it essential?
body: <p>I am in the process of learning ES2015 and I'm not fully understanding everything about classes. To my understanding you define a class like this:</p>
  
  <pre><code>class Parent {
    constructor() {
      // ...
    }
  }
  </code></pre>
  
  <p>and a subclass like this:
  (where super() must be invoked to initially run the constructor from the parent class).</p>
  
  <pre><code>class subClass extends Parent {
    constructor(name, description, url) {
      // subclass must call super to invoke the parent's constructor method
      super();
    }
  }
  </code></pre>
  
  <p>What exactly is the constructor method, why is it important, and why does a parents constructor needs to be invoked when creating an instance of a subclass?</p>