ES6-ify void-dom-elements-no-children rule and test file

[dfilipidisz]

I've seen in issue #1240 that using some new patterns from node 4 would be a nice addition.

Starting out I only updated the void-dom-elements-no-children rule and test file to use:

• const and let instead of var
• Arrow funtions
• Template literals instead of [].join()
• Some minor unification of formatting

I've also seen a comment in the rule file that using Set would be nice, which is also available with node 4. Can I make that conversion too?

Is this PR okay, and if so, is there a preferred way I should continue with updating?

[lencioni]

Thanks for the contribution!

As for updating the rest, I'd suggest automating the conversion in some way and also enforcing it with appropriate eslint rules where possible. I'd also recommend one commit per transfrormation across all files (e.g. one commit that changes var to const or let and enforces it via an eslint rule for all files). These are okay as separate PRs as well, which might help them get merged faster.

Some changes can be automated by enabling the rule and running eslint --fix, while other changes can be automated via codemod. (More info on this: https://medium.com/airbnb-engineering/turbocharged-javascript-refactoring-with-codemods-b0cae8b326b9).

[dfilipidisz]

Thanks for the review and directions on how to proceed! I'll look into how to utilize codemods for this and will keep each transformation in separate PRs.

[ljharb]

LGTM! and yes, using Map/Set is totally OK now that we require node 4+.