Support FileAttachment in local ES modules

[mbostock]

It’d be nice if you could use file attachments in local ES modules. I’m imagining it would work like this:

import {FileAttachment} from "npm:@observablehq/stdlib";

const foo = await FileAttachment("foo.csv").json();

In this case, the path foo.csv would be relative to the current ES module.

The dual meaning of importing the Observable standard library would be a little odd, though. I’m not sure how that would work… and maybe this is a pipe dream.

[mbostock]

This is probably hard, and I’m not entirely sure we want to do this (given the ambiguity of where FileAttachment comes from in the standard library). Let’s discuss before we get too deep here!

[mbostock]

I think we should prefer using fetch for interoperability with standard JavaScript, and we already detect local fetches in imported ES modules.