Return promise for decorator on async method

[rickh18]

After updating from 5.3.0 my application broke on a method that was returned a promise. It turned out that the instead of the promise, undefined was returned by the method, comparable to the behaviour described in issue #106.

This has been fixed by adding return fn in trackEventMethodDecorator.
The unit test now has an extra check to see if the original method still works.

[tizmagik]

Thanks, and great work! This makes sense -- I just had a couple notes inline.

Thanks also for adding a test to trackingEventMethodDecorator.test.js -- would you mind also adding an e2e test with an async use case? I tend to put more weight behind that suite since it's actually testing the external API.

[tizmagik]

nit: mind rewriting as:

.then(() => fn)

[rickh18]

Fixed with d7adf1f
I also added an e2e test as suggested.

When writing the test, I noticed that the tracking function breaks if a promise is rejected. It will fail on { value } since value is set to null after reject. So when using the example in the readme:

@track((props, state, methodArgs, [{ value }, err]) => { } <-- will give TypeError

.catch(error => { trackEvent(null, error); throw error; }); <-- trackEventMethodDecorators.js line 28, value is set to null

So the happy flow is working now, but maybe this should be fixed as well. (changing null to {}?)

[tizmagik]

Yea that makes sense, good catch! Mind making that change as a separate PR (will need an accompanying test update)

[tizmagik]

Thanks for this! (And apologies for the delay!)

[tizmagik]

Released as v7.3.0 -- thank you! 🎉