John Lenz

Are you using https://github.com/webpack-contrib/closure-webpack-plugin? In the abstract, without a plugin, this code is incompatible with Closure Compiler ADVANCED optimizations because from the compiler's perspective the definitions of "myFunction" are hidden...

Yes, setting it to 0 will tell it not to break at all.

I would like to see this added to assist in ES6 destructuring.

Unfortunately, the optional "map" function prevents this method from being marked as @nosideeffect. We need an annotation like "if the function is missing or known to be side effect free...

Looks like the polyfills are interfering with the analysis of the methods.

+1

We generally allow the compiler to perform optimization with the assumption that the code is correct (we allow the compiler to "fix" broken code). If this were a "let" instead...

Hmmm, I would have expected the VariableReferenceChecks to be on by default? How are you running the compiler?

Something is not right with the webservice as well, even with // @warning_level VERBOSE the warning is not presented: https://closure-compiler.appspot.com/home#code%3D%252F%252F%2520%253D%253DClosureCompiler%253D%253D%250A%252F%252F%2520%2540compilation_level%2520ADVANCED_OPTIMIZATIONS%250A%252F%252F%2520%2540output_file_name%2520default.js%250A%252F%252F%2520%2540formatting%2520pretty_print%250A%252F%252F%2520%2540warning_level%2520VERBOSE%250A%252F%252F%2520%253D%253D%252FClosureCompiler%253D%253D%250A%250Avar%2520x%2520%253D%25201%253B%250Avar%2520z%2520%253D%2520function%2520()%2520%257B%250A%2520%2520%2520%2520var%2520y%2520%253D%2520x%253B%250A%2520%2520%2520%2520var%2520x%2520%253D%25200%253B%250A%2520%2520%2520%2520return%2520y%253B%250A%257D()%253B%250Aconsole.log(z)%253B%250A%250A But it is in the debugger with "all diagnostics" enabled:...

Ah, that would be effectively the "third_party" flag which is always on for the webservice