Parcel: Support Web Workers coming from node_modules

[wojtekmaj]

Choose one: is this a 🐛 bug report or 🙋 feature request?

Both, I guess?

🤔 Expected Behavior

• node_modules should be also checked when looking for a file

😯 Current Behavior

• trying to refer to a Service Worker file from node_modules fails with the following error:

×  C:\Users\wojtekmaj\Projekty\react-pdf\sample\parcel\node_modules\react-pdf\build\entry.parcel.js: Cannot resolve dependency './pdfjs-dist\build\pdf.worker.js' (...)

what it is trying to do is look for the path in ./ but not in node_modules.

🔦 Context

💻 Code Sample

I'm currently working on support for Parcel in React-PDF. That requires me to handle loading a service worker which is not mine.

In Webpack, the following code does the job:

var pdfjs = require('react-pdf/build/pdf.js');
var PdfjsWorker = require('worker-loader!react-pdf/build/pdf.worker.js');

if (typeof window !== 'undefined' && 'Worker' in window) {
  pdfjs.PDFJS.workerPort = new PdfjsWorker();
}

I was trying to reproduce the same using Parcel, and here's what I got so far:

const pdfjs = require('pdfjs-dist');

if (typeof window !== 'undefined' && 'Worker' in window) {
  pdfjs.PDFJS.workerPort = new Worker('pdfjs-dist/build/pdf.worker.js');
}

This results in an error described below. Changing the line to

pdfjs.PDFJS.workerPort = new Worker('../node_modules/pdfjs-dist/build/pdf.worker.js');

stops the error, but:

• I'm not comfortable with relative path in a package like that
• This caused.. a 404 error! Parcel starts referring to a file it did not produced.

🌍 Your Environment

| Software | Version(s) |
| ---------------- | ---------- |
| Parcel |1.5.0
| Node |9.3.0
| npm/Yarn |npm, newest
| Operating System |Windows 10

[wojtekmaj]

Here's my full code at the moment if you'd like to have a look:

https://github.com/wojtekmaj/react-pdf/tree/parcel/sample/parcel

[devongovett]

Ah this is an interesting issue. We treat the argument to Worker as a URL, which it can be. That means this is being treated as a relative path rather than a Node module path. We could maybe require the path to start with ./ or ../ in order to be relative? Not sure we can change this everywhere URL paths are used though since relative URLs without that are fairly common.

[wojtekmaj]

Actually that would be great. Not having ./ in front of the path suggests that the path either:

• is a path to node_module
• is a path set in jsconfig.json in compilerOptions.paths field as kind of a "root" directory

I'd greatly appreciate this improvement. I'm really looking forward to support Parcel :)

[mischnic]

The correct term would be web worker. Service workers handle caching and push notifications.

[wojtekmaj]

Guys, is there any news regarding that matter?

I'd really like to officially support Parcel in React-PDF, but I'm super unsure about web worker necessary for my project to run correctly. It seems like my workaround is doing the trick, but to me it looks just messy. Is there an official, recommended way to handle this?

[mischnic]

@devongovett Inspired by the new resolver:

• "~/node_modules/pdfjs-dist/build/pdf.worker.js" for "[../]node_modules/pdfjs-dist/build/pdf.worker.js"
• "lib/worker.js" = "./lib/worker.js" for relative paths

[devongovett]

For Parcel 2, we are considering supporting an npm: URL protocol to resolve node_modules instead of as a relative path. For example:

new Worker('npm:pdfjs-worker');

Without the npm:, it would resolve the same as ./pdfjs-worker, since it is a URL.

See https://github.com/parcel-bundler/parcel/issues/3492#issuecomment-529120998 for more details.

[MikeYermolayev]

Looks like I have some similar issue.
I'm trying to use a node_module which uses a worker-loader and get the error below.

Are there any workarounds? Really don't want to switch to webpack because of that issue(((
Thanks in advance

[devongovett]

worker-loader is a webpack specific tool and won’t work with parcel. You can construct a worker like this:

new Worker(“./worker.js”)

[mischnic]

@MikeYermolayev I fear there's nothing you can do here. (And I think publishing code with worker-loader calls is bad for exactly this reason).

[MikeYermolayev]

@mischnic yep. Had to reject using that library