Very high memory usage compiling mozilla/PDF.js

[abonckus]

Bug Report

Current Behavior
When running npm start or npm run build, while pdf.js is used in create-react-app project, memory usage seems to skyrocket to unreasonable amounts and fail with "JavaScript heap out of memory" error.


I've reported it to PDF.js guys, and they found that ejecting and downgrading babel from 7.7.0+ to 7.6.4 seems to fix the issue so they think it must be regression issue with Babel. The issue can be reproduced in any fresh create-react-app (version 3.3.0) project with pdfjs-dist installed. (link to original issue)

Steps to reproduce the problem

1. Create new react app with create-react-app
2. npm install pdfjs-dist
3. Copy example
4. npm start or npm run build

Input Code
Example repo

Expected behavior/code
npm start or npm run build succesfully without unreasonable memory usage

Babel Configuration (babel.config.js, .babelrc, package.json#babel, cli command, .eslintrc)
No additional configuration except of what CRA gives us

Environment

System:
    OS: Windows 10 10.0.18362
  Binaries:
    Node: 12.13.1 - C:\Program Files\nodejs\node.EXE
    npm: 6.13.4 - C:\Program Files\nodejs\npm.CMD

• Babel version(s): v7.7.4
• Node/npm version: Node 12/npm 6
• OS: Windows 10 Enterprise 1903

[babel-bot]

Hey @artisb45! We really appreciate you taking the time to report an issue. The collaborators on this project attempt to help as many people as possible, but we're a limited number of volunteers, so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack community that typically always has someone willing to help. You can sign-up here for an invite."

[midgethoen]

I just realise I commented underneath the wrong issue.

I have patched the file described in the PR, but this doenst fix the memory error for me.

FYI, however, by deleting the sourcemaps from the pdfjs-dist package i can get CRA to run again.

[JLHwung]

Update: The issue is not fixed since I misidentified the memory bottleneck.

For CRA users, you can remove the source maps from the pdfjs-dist package (thanks to @midgethoen).

Babel 7.6.4 works because inputSourceMap is not functioning, which is later fixed in #10623. However inputSourceMap bloats the memory via JSON.parse/JSON.stringify on this big source maps (3.13MB) in pdfjs-dist, just in order to merge this source map with the source map generated by babel transform.

[midgethoen]

Thnx for the quick response @JLHwung. Hopefully I can test the patch out later today.

[midgethoen]

Huzzah 🎉 it has been fixed for me. thnx again.