Add caching ability to the loader

[genintho]

While webpack is great to pick up only incremental change, the compilation time at lunch can be very long. For our application, it takes minutes, which means it takes minutes before our tests can run, before we can deploy, before developer can start working when starting their day.

I did similar changes to the coffee-loader, or the Uglify plugin, saving huge chunk of time.

Cache the eslint result into a file.
The input is hash using MD5 to detect changes.

{
    "path.js": {
       "hash":"7c451761c8712467357cd5750e303d1f",
       "res": "what_ever"
}

This cut 30% of my webpack build time.

If this PR is accepted, I am happy to update the documentation and write a few tests.

Fixes #82

[genintho]

Please ignore the CI status, I will fix this if the idea behind the PR is approved.

[MoOx]

Maybe you can post some benchs (without cache, with cache)?
For the cache folder, it can be nice to simply use https://www.npmjs.com/package/find-cache-dir
If benchs prove to be useful, then I am ok with this feature.

[genintho]

Eslint process 220 files

run 1: no cache
run 2: no cache
run 3: cache on -> compute it
run 4: cache on
run 5: cache on

The more file you process, the bigger the wins are.

[genintho]

I updated the PR too

[MoOx]

Looks good!
Can you add some doc in the README please?

[genintho]

I will. It will be a little delayed, I am in vacation for now :)

[MoOx]

@genintho np, enjoy ;)

[genintho]

Documentation added.

[MoOx]

any reason you don't require() the file instead?

[genintho]

I am not sure. Is it better?

[MoOx]

Better I can't prove it, but definitely shorter :)

This should be enough:

try { 
  cache = require(thunk("data.json"))
}
catch (e) {
  cache = {}
}

[genintho]

updated.

[MoOx]

Thanks. Sorry for the delay. Will cut a release.

[genintho]

Woot!

[genintho]

So one piece of feedback regarding the usage of find-cache-dir. The library is not really solid as the path of the cache directory it find depends on where you are when you run the webpack process. So doing things like node ~/oneDir/2ndDir/3rdDir/myconfig/build.js is not caching at the same location (and in fact can throw errors) than doing node myconfig/build.js .

[MoOx]

@genintho maybe we can add a way to specify a folder? Default to find-cache-dir, and ability to specify one?

[gaearon]

I think it would make sense to use the same caching strategy as babel-loader uses since it’s been tested thoroughly.

[MoOx]

Indeed! Would be nice to have this as a module ;)

[gaearon]

Unfortunately, this implementation misses some of the essential error handling that babel-loader provides. Would you be interested in fixing this? I posted a small analysis in facebook/create-react-app#1656 (comment) after this caused issues for Create React App users when we enabled it by default.

[MoOx]

I personally don't have time for this but maybe someone else will. Feel free to open an issue as a reminder until someone handle it.