Adding a sensor element

Now what we want to do is make is to that when we scroll to the bottom of the page, we add the next 4 items to the products array.

So how do we detect if we're at the bottom of the page? Most browers offer an API that allows you to query an element and see if it's currently in the viewport or not.

So let's put an invisible element at the bottom of the products list and use this as a sensor.