We do this a couple times; we could definitely do this once and remove meta and reuse that array. If we're mostly going to be doing iteration, we could just map over the keys and turn them into values, so end up w/ an array of languages. If we want to go a step further, we could tag the objects w/ a loading property and remove the withoutDependencies information and just recurse until you hit a component that's already being loaded.

This would be a bit more stateful but shouldn't be hard to implement and would allow us to hide the implementation details from consumers. I don't really love exposing withoutDependencies, if if it's not technically public API, and that would do away with it nicely.

I'm not sure I understand your whole idea here.

We could indeed process the languages only once, though. We could build a structure that maps a language to its "peerDependencies" and therefore just access it by key. Something like:

var dependentsMap = null;
function getOptionallyDependents(mainLanguage) {
    if (!dependentsMap) {
        dependentsMap = {};
        /* Build a structure like:
        dependentsMap = {
            "fortran": ["pure"],
            "coffeescript": ["haml", "pug"],
            ...
        }
        */
    }
    return dependentsMap[mainLanguage] || [];
}

Is it what you meant?

If we change this to:

if (!components.languages[language]) {
  console.warn('Language does not exist ' + language);
  return;
}

...then we can save an indentation. I like early returns :)

peerDependencies maybe?

One-liner these two?

Is the purpose of withoutDependents to avoid an infinite loop? Are we sure it recurses through everything? If it is, maybe we don't need it (see above).

Actually no, it wasn't to prevent an infinite loop. I think an infinite loop can still happen if we have circular dependencies, hopefully this is not the case at this time AFAIK.

It was supposed to be an optimisation, because you need to reload a component so that it takes its updated "peerDependencies" into account, but you don't need to reload the whole "inheritance" tree. There's already a lot of files being required there, so I tried to keep the amount as low as possible.