v5: Linting / Code styles

[oliverfoster]

Subject of the issue

• Remove jscs and jslint as jscs is deprecated
• Use eslint or an eslint derivative (https://standardjs.com/#standardjs--the-rules or https://github.com/standard/eslint-config-standard/blob/master/eslintrc.json)
• Add npm/grunt task to allow systems integration

[oliverfoster]

I'm not sure about using standardjs as a package. I think if we stick with eslint and start with the standardjs config removing the no colons requirement.
All of us use colons, it'll get in the way even though it makes a lot of sense to only use them where they're necessary.

[tomgreenfield]

Current reference: https://github.com/adaptlearning/documentation/blob/master/01_cross_workstream/style_guide.md.

[nilslp]

Current reference: https://github.com/adaptlearning/documentation/blob/master/01_cross_workstream/style_guide.md.

Is this something that we will need to keep or will we be running with the standard eslint config as @oliverfoster has mentioned?

[moloko]

@nilslp i’d be tempted to keep that so that people can view the style guide in ‘human readable’ format rather than having to work through a config file trying to figure out what the rules are

@oliverfoster agree that eslint looks like the better option

[oliverfoster]

@nilslp found https://prettier.io/ which is a code formatter rather than a linter. It's got good integration with editors and git hooks.
Instead of requiring people to code in the right style the style will be applied automatically, on save with an extension or on commit with git hooks.
It doesn't do linting so won't help with errors but it does apply the style instead of reporting it and it does all the languages we need, whereas ESLint only does JS.
Might be a better idea?