ES6 refactor

[jbienkowski311]

This pull request is a first step to move this project closer to the present times.

Description

1. Refactor ZooKeeper and its promisified version to ES6 standard.
2. Get rid of lib/promise, instead use native Promise class.
3. Fix tests, so they pass.

Motivation and Context

This project remembers the old days of Node 0.x. A lot has changed since then and we should move on. This PR is a first step towards better code quality.

As there are a lot of changes I submit this PR as is for now. I will however start working on enforcing the eslint rules, so we should end up with a project that is nice and tidy.

TODO

• Make eslint pass
• Explicitly define API input parameters

How Has This Been Tested?

It has been tested with both unit and integration tests.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have read the code of conduct.
• I have read the contributing guide.
• I have updated the documentation accordingly (if applicable).

[DavidVujic]

Thank you for doing this long awaited task! It's a massive PR and I will need some time to review this.

[jbienkowski311]

You can follow ESLint refactoring progress in a separate PR: jbienkowski311#1

[DavidVujic]

Awesome work @jbienkowski311!

[jbienkowski311]

I've merged eslint branch and resolved the conflicts. I did not enable ESLint rules on tests_integration directory - it is a lot of work to make it pass and I do not think that it is worth the effort. After all, it's just a bunch of tests.

What I would like to do before announcing that this PR ready to merge is explicit definition of the input parameters for the API methods. Before, the library was using arguments, right now I use ...args as a temporary solution to make ESLint pass. However I believe in rule that explicit is better than implicit 😉

PS: You can consider #184 as done 😉

[jbienkowski311]

Okay, I think that's enough for this PR. @DavidVujic please check if I did not mess up with the API (I used documentation from README.md and tests). I've added a_sync method to the documentation as it was missing. Not sure if it's correct though... 😉

[DavidVujic]

Thank you @jbienkowski311! I'll have a look. I would like to finish issue #153 and build a new release from it before merging this branch. Are you ok with that?

[jbienkowski311]

Sure thing!

[DavidVujic]

Great work! I have a question about the legacy Promise library that is used in the Master branch: this PR with native Promises will be a breaking change, won't it?

If possible, to avoid breaking changes - could we add wrappers in the ZK Promise class for the old Promise lib functions? They could be marked with JsDoc "deprecated" comments. What do you think about it?

[jbienkowski311]

Great work! I have a question about the legacy Promise library that is used in the Master branch: this PR with native Promises will be a breaking change, won't it?

If possible, to avoid breaking changes - could we add wrappers in the ZK Promise class for the old Promise lib functions? They could be marked with JsDoc "deprecated" comments. What do you think about it?

Now this could be a potential breaking change... However it is an easy fix to implement. Just give me few hours 😉

[jbienkowski311]

@DavidVujic I brought back the ZkPromise class with previously missing methods being deprecated as suggested. There was one method that I was unable to restore - Promise.wait. The good news is that it would not work anyway 😉 I have covered new ZkPromise class with tests as well.

[DavidVujic]

Awesome! I'll try to finish the review in the next couple of days. Currently at a location with a poor connection 🐮 🐑 🐔 🇸🇪