Discussion on: What the beep is 'this' in JavaScript

[Brit Hemming]

This is likely a scope issue. A couple of things to know about classes:

• classes are not hoisted - that means if we are putting our information above a class we have referenced it will not work
• they use strict - it prevents window binding, forces us to write cleaner code with errors if we do not
• Methods are a special syntax
• A constructor function is visible

In your case point 1 is the issue - classes are not hoisted. You've created Handler below where you are invoking it.

Here's a codepen where I explain classes a little deeper. Hopefully that's helpful :)

codepen.io/BritHemming/pen/WNvYJMr