Javascript - Determine Child Event Occurred On

Currently I'm working on a personal project wherein I create a reading schedule, determining progress through a given book and whether or not the user is "on track" for completion. Currently the project is mostly functional, with an event handler activating and working as intended for each list element (representing a page or chapter). However, in order to determine whether or not the user is "on track" or not it it is necessary to know which numbered child was activated (for instance, the 50th child out of a 100 page book). Though each child is given a number when generated by JavaScript I'm not certain how to go about extracting that number into a variable, so that I can use it for comparisons.

Snapshot is here: https://w.trhou.se/nr01qk06lu

This program is written in Brackets, and because of this Treehouse's preview feature is a little awkward with it. To view the page itself you have to navigate through the directory a little, or you can simply download the files and view them that way.