Feature Request: Add resolvers for module named packages for offline support

[brion-fuller]

Currently, module-resolver only works for a CDN like unpkg or using alias. We should give the ability to resolve module named imports to the node_modules folder.

Example

import { LitElement, html, customElement } from "lit-element";

@customElement("hello-world")
export default class HelloWorld extends LitElement {
  render() {
    return html`<h1>Hello World</h1>`;
  }
}

This could resolve to the /base/node_modules/lit-element/lit-element.js

[l1bbcsg]

Sounds fair.
I believe we didn't think about it because ECMAScrript modules support in node is still experimental and we tried to use production version of dependencies, therefore avoiding exporting from node_modules.
I don't see why it can't be added as an option to the preprocessor though.

It's probably pretty trivial to implement with require.resolve too.

One thing that may go wrong is that Karma will need to serve files from node_modules and those files may be anywhere in the filesystem, potentially even above Karma/project roots (think global installations) and this might get weird because of the way it does absolute paths.