Browsers compatibility fix

[scottinet]

Description

While scanning this SDK code to fix an unrelated documentation issue, I came across a process.nextTick call, which is a pure-NodeJS method.
So, I fixed that. Which led to a failed unit test, also relying on process.nextTick.

It came to me that having a browser-compatible code tested with ES6 and/or NodeJS specific code was not a good idea, so I modified ESLint to make sure our code and tests are using the same standards, and reverted unit tests from ES6 to ES5.

[codecov-io]

Codecov Report

Merging #184 into 4.x will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##              4.x     #184   +/-   ##
=======================================
  Coverage   99.39%   99.39%           
=======================================
  Files          16       16           
  Lines        1665     1665           
  Branches      441      441           
=======================================
  Hits         1655     1655           
  Misses         10       10

Impacted Files	Coverage Δ
src/Kuzzle.js	99.45% <100%> (ø)	✅

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e60778e...8199d21. Read the comment docs.

[xbill82]

I don't understand the point of this PR, since the code is transiped by Webpack and in the README we tell developers to use the transipled version in dist for the browser so... All the nextTick are automatically transpiled to setTimeout(..., 0) by Webpack, making the transpiled code ES5 compliant.

[scottinet]

We certainly use webpack, but there is no transpilation, everything is in pure ES5, and webpack uses the code as is to create the minified SDK version.

This was a choice made a long time ago, but now this is a choice I regret. One day I'll rewrite everything in ES6 (or even ES7 if I make my mind late enough) and use a transpiler.

Moreover (to be checked), I'm not certain that transpilers can transpile NodeJS-only methods, and process.nextTick is one of them.

[xbill82]

Ok, I understand.
As an aside, I can reasonably say that Webpack can translate node-specific methods to browser-specific ones. This was the aim of Browserify, which Webpack reproduces.