In pretty much all of my games (including brand new games without any character sheets/API scripts attached), I notice that there are several instances of this error in the developer console: app.js?1509570495:41 Uncaught TypeError: t.data.substring is not a function(…)t @ app.js?1509570495:41
Although the error seems benign, it may be worth cleaning up. After unminifying the code, I tracked it down to a web worker message event handler. The issue could easily be fixed by making sure t.data is a string (e.g. typeof t.data === 'string') before calling t.data.substring() in the handler's else-if conditional. :)
