mima | A tool for catching binary incompatibility in Scala | Build Tool library

In fact you can even implement/override a def with an object in a subclass.

This will work as long as the species names are consistently spelled. Assuming your sample data is called species:

First of all, u have typo on getElementById() void, it should be .member rather than .members. After your randomElement variable needs to be into your function, otherwise return value of this variable will be always the same. And finally, you can directly access your properties object dataArray thanks to randomElement variable in order to set your content. Complete code :

What is happening in your codepen, is that when you send a member function as parameter to something which will store it and use it later (an event listener will store the function in an internal variable, and call it when the event is fired) in JS, this member function "loose" the this property. It is not linked to lit-element but on the js itself, and can happen in a variety of case, but lit-element create many case where it can become revelant.

You can use

document.addEventListener('click', e=>this.handleDocumentClick())

instead of

document.addEventListener('click', this.handleDocumentClick)

The arrow function will instruct JS to bind the 'this' of the object in which it is declared, and then call the member function with the correct context.