TypeScript inside the package

[artospaj]

I've done a TS mapping to be able to use the mqttsn-packet in my project and I'd like to share the results with you.

[artospaj]

@ithinuel could you please take a look?

[ithinuel]

Thanks for your contribution, I'm glad it can help you !

I don't know much about typescript so I have some questions:

• Is there a way to test the validity of those new files ?
  eg, checking the APIs actually match and are not broken by futures changes ?
• Can those test be tested in CI ?

Speeking of CI, I noticed that the nodejs versions in .travis.yml where long outdated. So I prepared #4 to bump them to latest version and latest LTS.

[artospaj]

@ithinuel thank you for pointing out the question regarding type validation, I've taken some time to verify what's possible and found out it can be partially done using:

npx tsc --allowJs --checkJs ./mqttsn.d.ts ./packet.d.ts

This led to few issues being fixed 🙇

Unfortunately, that's only a semantics and for sure it can let some logical errors pass. The only way I can know is to rewrite tests to TypeScript, to let compiler jump in when it detects any difference in types when API methods are used in test scenarios.

[ithinuel]

Thanks for looking into this.
Would you mind updating .travis.yml to add that check ?

Do you think it'd be reasonable to add a little .ts example to demo this lib using typescript ?
This could be run in CI to have at least a minimal typescript subset being tested.
EG: have SubscribeShortTopic turned into a Buffer and parsed back into an object ?

I could then use that as a reference if/when I find time to learn typescript 😄