Error when running my custom visual in Dev Tools

[mash]

I am looking for help on an error message I get when I copy my code for my custom visual from Visual Studio and paste it into Dev Tools.  When I look in the browser's debugger I get a error of "Unable to get property 'sourceCode' of undefined or null reference TypeError:  Unable to get  property 'sourceCode' of undefined or null reference at y".

Is there any documentation I can read that would help me better understand these errors?

[mhardy]

I've also had a lot of issues pasting VS code into dev tools.  The biggest issue I've found is DevTools doesn't support let and const.  These all have to be replaced with var.  Unfortunately re-scoping variables like this can have some adverse side effects.

Not sure this is your issue but worth a look.