using process.exitCode instead of process.exit()

[davidkwan95]

This PR should fix issue #2716

[codecov]

Codecov Report

Merging #2717 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #2717   +/-   ##
=======================================
  Coverage   35.51%   35.51%           
=======================================
  Files         434      434           
  Lines        9501     9501           
  Branches      986     1009   +23     
=======================================
  Hits         3374     3374           
+ Misses       5467     5459    -8     
- Partials      660      668    +8

Impacted Files	Coverage Δ
app/react/src/server/build.js	0% <0%> (ø)	⬆️
app/vue/src/server/config/babel.js	0% <0%> (-100%)	⬇️
app/react/src/server/babel_config.js	0% <0%> (-76.67%)	⬇️
app/polymer/src/server/utils.js	0% <0%> (-53.58%)	⬇️
.../ui/src/modules/ui/components/addon_panel/index.js	34.78% <0%> (ø)	⬆️
app/react-native/src/preview/story_kind.js	0% <0%> (ø)	⬆️
addons/a11y/src/components/Report/Info.js	0% <0%> (ø)	⬆️
...modules/ui/components/stories_panel/text_filter.js	30.98% <0%> (ø)	⬆️
lib/ui/src/modules/ui/components/shortcuts_help.js	12.85% <0%> (ø)	⬆️
lib/ui/src/modules/ui/containers/layout.js	12.5% <0%> (ø)	⬆️
... and 52 more

---

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 402183b...a4f2768. Read the comment docs.

[ndelangen]

Thank you for this PR, Looks good. Can you teach my why the issue occurred and why this fixes it?

[Hypnosphi]

I'm intrigued as well. Docs actually say that using process.exit() is not a recommended practice, but the reason is that it may force the exit too early which is contrary to the referenced issue

[davidkwan95]

I'm not too sure, but I noticed that calling process.exit() inside the callback function seems to wait for some process to be finished before exitting. I'm assuming it has something to do with webpack or node.
Without calling the process.exit(), we will be able to exit the program after the event loop is done, but since we got an error, we need to set the exit code to 1 by using process.exitCode = 1

[Hypnosphi]

after the event loop is done

If there's some async process running, event loop won't be done until the process is finished. Did you check if your fix is working?

[davidkwan95]

I've checked that the fix works in my current project.

[ndelangen]

So I've actually hit this problem now on an other library.
danielstjules/jsinspect#69

I'm ready to approve this.