style: prefer const

[domoritz]

There are still many places where we can't use const because multiple variables are defined with a single var/let but we can fix those later.

Maybe we can run a codemod (https://github.com/facebook/codemod) to upgrade all of the code automatically. But at the same time we should probably switch to prettier and babel.

[domoritz]

cc @lgrammel

[lgrammel]

Hey! Maybe some background on my pull requests, it was a dry run for an automated tool (Jeff suggested trying it out on Vega). It's similar to codemods. I could actually implement a split of let statements that define multiple variables, some of which could be const if there's interest?

[domoritz]

Awesome. Yeah, I would love to have a more consistent code style between the different Vega projects.

I recently submitted a pull request to d3 scales to use let/const (d3/d3-scale#212). The other d3 repos still need to be updated (d3/d3#3435) so there may be interest beyond Vega for your tool.

[lgrammel]

Cool, thanks for the pointer. I'll see if this works for the d3 repos as well.

[lgrammel]

@domoritz I've run 3 codeshifts (var -> let/const, arrow functions, object property shorthands) that would result in roughly ~500 changes. Is this something it would make sense for me to create PRs for? And if so, how would those PRs ideally be sized (e.g. per file/codeshift, for all files at once (one PR per codeshift), some intermediate slicing (e.g. per directory)?

[domoritz]

I'd be happy with one pull request for everything since all the changes are of the same kind. But I'll defer to @jheer for deciding on what goes into master.

[domoritz]

Also see #2827