Improve error message if observer is missing

[robdodson]

If I define an observer on my properties object but don't actually implement the method, I get a strange error in effects.html: Uncaught TypeError: this[effect.method] is not a function. It's really not clear that the issue is a missing observer, I had to track down @cdata who could point me in the right direction. Any chance to handle and send out a helpful error message in this scenario?

[lrbridge]

+1

[kevinpschaaf]

Yes, we'll be doing a "useful warning" sweep and adding warnings for some obvious things. For user errors that don't make the cut for having warnings included in Polymer proper, the work-in-progress polylint tool will be much more exhaustive.

[jmcgdz]

+1