Is the fmFetch-Demo busted at the moment? Running it and on clicking Fetch Data yields the error:
Unhandled Promise Rejection: Error: Could not call script, ‘GetSimpleResult’. ‘window.FileMaker’ was not available at the time this function was called.
I cannot replicate that behavior in the demo file, but this error can show up if the FileMaker Pro client has yet to inject the neccesary JavaScript into the WebViewer.
If you load the demo URL in your browser, then you would expect to get that error, since FileMaker will only inject it’s function into a WebViewer on a FileMaker layout