Issue #582: Add ESLint to package.json test script

[ChristianMurphy]

'posttest' automatically runs after 'npm test'

[vertein]

I like it. We have some merge conflicts now.

[ChristianMurphy]

@vertein Resolved merge conflicts

[ChristianMurphy]

📓 Note that the Google styleguide recommends some ES6 features be preferred over their ES5 counterparts.
If you do not want to drop ES5 support or add a transpiler the ES6 rules should be disabled. 🚫

[apetro]

I admit to a lack of expertise in ES best style practices.

I nonetheless passionately believe that we should just adopt whatever Google Style is, and do so with a minimum of exceptions.

[ChristianMurphy]

The difference from a project standpoint is browser compatibility.
These are the feature Google code styleguide recommends, and how they are supported in mainline browsers.

Browser	Arrow Functions	Let/Const	Rest/Spread	Generator Functions/Yield
Chrome 57	✅	✅	✅	✅
Firefox 52	✅	✅	✅	✅
Edge 13	✅	✅	✅	✅
Safari 10	✅	✅	✅	✅
IE 11	⛔	⛔	⛔	⛔

Source: https://kangax.github.io/compat-table/es6/ ◀️ also lists support in beta and some legacy browsers.

[thevoiceofzeke]

We can't drop support for IE, so we're going to have to disable the es6 rules from the google plugin. Adding the following to the "rules" block takes care of it:

"arrow-parens": 0,
"constructor-super": 0,
"generator-star-spacing": 0,
"no-new-symbol": 0,
"no-this-before-super": 0,
"no-var": 0,
"prefer-rest-params": 0,
"prefer-spread": 0,
"rest-spread-spacing": 0,
"yield-star-spacing": 0

Merging as-is would break MyUW in IE

[ChristianMurphy]

Thanks for following up @thevoiceofzeke!
I've updated the PR to remove ES2015+ recommendations from the linter.

[coveralls]

Changes Unknown when pulling 7cd7713 on ChristianMurphy:eslint into ** on UW-Madison-DoIT:master**.