ModX Revolution - custom work drop down list. How to make scripted activation?

Question

JavaScript

It's on the Extras tab. gender (in the admin), for example, the drop-down list Authors.
Each author has his own documents.
There is a second drop-down list - Documents.
Is it possible to make it so that when an author is selected in the first list, only the documents of the selected author are loaded in the second?

Answer 1

Doper.
https://jsfiddle.net/salofun/a1dzz009/1/
Thank you all.

Answer 2

the logic is something like this: you can move the pointer to the end of the array (using end), get the last key.
if the current key is not the last, output a comma (if ($key !== $last) echo ',';