[WIP] Linting with eslint and husky

[azerella]

As drafted by @toxamiz in #700, this is a more workable branch.

Issue reference: #429

Todo:

• [ ] JavaScript linting needs to be IE8 compliant.

[toxamiz]

@adamzerella, What you think about https://github.com/govau/design-system-components/pull/700#issuecomment-478085818 ?

Summary easy way to make js code IE8 compliant: stick with es5 syntax and recommend users to apply polyfills if they actually need an IE8 support es-shim, DOM-shim.

Or start to use transpile or even some of bundler (rollup etc.) on module.js.

jQuery includes some polyfills as i know, so actualy don't need to do anything here (just es5 and jQuery API).

[azerella]

We don't have a choice when it comes to IE8 support, it's something that we support @toxamiz.

We might need to create a IE8 complaint eslint-plugin to resolve this ticket. We need to be able to write code that provides our developers with linting without relying on polyfills.

[toxamiz]

@adamzerella but you already using and relying on polyfills. In every test file you have html5-shiv and media-query polyfill for breakpoints from core globals (AU-media). For example grid-12 wouldn't work in ie8 separately if developer wouldn't apply media-query polyfill manually.

Can you explain, please, why you are refusing to use ie8 polyfills here? es5 requirement and polyfills for ie8 will solve this problem.

[azerella]

@toxamiz We are relying on polyfills where it makes sense. We are currently using html5shiv.js and respond.js as you've seen in the test/ files. This provides HTML5 and media functionality for older browsers. We do not ship the components with any shiv / shim libraries.

Linting and shivs are unrelated to one another. We need a way to lint our vanilla JavaScript so that it's extremely compatibility across browsers, this means linting for things like using for( ... ) over forEach or issues like var over const / let.

You're right in saying we could just polyfill when we transpile the vanilla JavaScript but this isn't always going to work ( babel isn't perfect ) and it would increase our bundle sizes.