Terminology: Loader Phases

[jkrems]

I'm not sure if this is a better fit for terminology or for a more implementation-focussed discussion. But I would suggest a separation of concerns when talking about module loading. The outcome would hopefully be a clear description of what happens when and what phases are responsible for which concerns.

One possible variant of this can be found here: https://github.com/jkrems/loader#module-loading

For ease of discussion, inlining the content below:

Module Loading

Module loading is split into three phases:

1. Module resolution
2. Resource fetching
3. Module init

Module Resolution (resolve)

Given a specifier: string and referrerURL: string,
provide a url: string or a set of potential urls: string[] of a resource:

const resolve: (specifier: string, referrerURL: string) => string | string[];

Resource Fetching (fetch)

Given a resource url: string,
fetch the resource content and associated meta data.

type Resource = {
  bytes?: Buffer,
  contentType: string,
  contentTypeParameters?: string,
};

const fetch: (url: string) => Resource;

Module Init (init)

Given a resource: Resource and a target: Module module handle,
initialize the target.
Most implementations will check the resource.contentType
to select the appropriate behavior.

const init: (target: Module, resource: Resource, Module) => void;

[jkrems]

Custom MIME types could be supported by a fetch hook:

async function detectTypescriptFetch(parent, url) {
  const resource = await parent(url);
  if (resource.contentType === null && /\.ts$/.test(url)) { // "unknown contentType"
    resource.contentType = 'typescript';
  }
  return resource;
}

[SMotaal]

On that example, I would also consider:

1. no extension
2. url including query or fragment

Did you think of ways to deal with those?

[jkrems]

@SMotaal That's an orthogonal concern. The above was meant to illustrate handling a content type that isn't covered by a built-in mime DB. Handling query or fragments is fairly simple and doesn't change anything fundamentally. No extension will always require an additional out-of-band signal. :)

[SMotaal]

#208 relates if we have a "ModuleSourceText" interface that can be used to end the fetching portion (ie resolve blesses it, fetch allows it)

[jkrems]

Replaced by #232