Things to clear up before jumping into the world of React

super.md

3. How "super" keyword works in JS

The main issue that we will come across in React is the usage of "this" in constructor.

This issue can be summarised as follows:

The JS engine only attaches an object instance to the context variable (this) once you get to the highest prototype in the chain - which is Object

  class Widget extends Resource {
    constructor() {
        console.log(this);   // ReferenceError
        super();
    }
  }

For more info, go here