Refactor to use Typescript

[wemeetagain]

Refactored to use typescript with minimal changes to process and code.
Imo, using typescript in this project will pay dividends as the gossipsub feature-set grows. It becomes much easier to reason about this codebase which has many moving parts and datatypes when there's that minimal level of type/sanity checking.
That said, I attempted to do this update in a way that's minimally invasive to the standard libp2p workflow.

• typescript code lives in ts/, gets transpiled to src/
  • prebuild and pretest scripts runs tsc
  • build step left untouched - aegir build
  • emits js code in strict mode
  • pubsub.js left untouched (expected to migrate to js-libp2p-pubsub repo eventually)
  • src/ not checked into git, like dist/
• built dist/index.min.js is 2KB larger, from 468KB to 470KB
• linting now performed by eslint (using standard and @typescript-eslint configs/plugins) instead of aegir, as the typescript files themselves are to be linted
• tests left untouched
• caught a few bugs
  • doc strings out of sync
  • no null checks for nullish values
  • improper use of functions due to misleading variable names
• GossipSub => Gossipsub throughout (I can remove to future PR if desired)
• types in ts/peer.ts should eventually go to js-libp2p-pubsub

[codecov-commenter]

Codecov Report

Merging #77 into master will decrease coverage by 5.68%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #77      +/-   ##
==========================================
- Coverage   85.68%   80.00%   -5.69%     
==========================================
  Files          11        1      -10     
  Lines         510       10     -500     
==========================================
- Hits          437        8     -429     
+ Misses         73        2      -71     

Impacted Files	Coverage Δ
test/utils/index.js	80.00% <ø> (ø)

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[mpetrunic]

Since you are using typescript it would be useful if you add public/private/protected modifiers so we can navigate easily when extending in lodestar

[wemeetagain]

@vasco-santos Thanks for bringing up the larger issue of standardizing the tooling and strategy for supporting typescript across the js-libp2p/js-ipfs ecosystem.

I do think that using full typescript here will be beneficial, over, eg: autogen declarations. Imo it mainly boils down to improved dev tooling and type-checking sanity checks. I think the benefits outweigh the additional machinery and differences with other libp2p repos.

The current gossipsub codebase has many rough edges and using typescript here clears up many ambiguities. As part of this process, several bugs were found just from having type-checking. While these bugs were obvious in hindsight, those particular issues would have never passed the base level of scrutiny we get using typescript. I'd love to see this gossipsub implementation be polished and be easily shown to be correct, and I think type-checking plays a role here.

The dev tooling aspect is also useful to call out. I've been working on gossipsub v1.1 in a local branch, and having the full IDE type-checking/hinting and autocompletion significantly reduces the mental burden of eg: spelling out logic with app-specific datastructures. We're able to declare datastructures with interfaces (in the case of gossipsubv1.1, these interfaces can be fairly large and wordy) and seamlessly use these to aid development without having to navigate opaque objects by hand. Using vanilla js, I was struggling to have my IDE link JSDocs throughout the project, and having to manually check for typos and correct usage, so the experience was not nearly so pleasant.

Remaining thoughts are how to best do this PR w/o negatively impacting the js-libp2p ecosystem and with maximal standardization/collaboration with the js-libp2p ecosystem.

I would love to keep using aegir where possible, (using it for linting eventually, if/when supported), and the current structure is an attempt to simply extend the current processes to a typescript codebase. Ideally after ts => js transpilation/pre-processing, "things can be treated the same".

Perhaps this may be the only js-libp2p repo using typescript, but I would like to get this right to maximally align with the whole ecosystem so it doesn't have to be treated strangely and can benefit from standardization.

[vasco-santos]

@wemeetagain thanks for exposing your thoughts. I agree with your thoughts and we should move on the way you are working on!

[vasco-santos]

LGTM!

[vasco-santos]

FYI, just released 0.4.3 with this PR and a custom aegir on my local machine to skip the dirty validation