How to trigger activities when elements become first visible?

[mkroetzsch]

It would be good if SQID would defer API calls and queries that are not necessary to create the initial display until they are really needed. For example, one could fetch references of each incoming statement when the user first opens the statements to see them. There are many other things that one could do when a statement is opened, but which should not be done for all statements upfront.

What is the best way to trigger actions that have to happen when a div first becomes visible? Is there a simple JavaScript/angular solution for getting this event? If would of course be possible to trigger this when we change the visibility of a div, but then the parent div needs to know which child elements would like to do something when becoming visible, creating a lot of overhead. It would be nicer if parts of the page could define such behaviour locally, i.e., if they could add (angular) HTML that makes sure a function gets called on first display.