Duplicated modules in output file

🐛 bug report

In my TypeScript + React project I’ve faced the problem with duplication of module in output JavaScript bundle. Same class imported two times.
Project is monorepo maintained with Lerna.

🎛 Configuration (.babelrc, package.json, cli command)


  "presets": [
        "targets": {
          "browsers": [
            "last 1 Chrome version"


  "private": true,
  "version": "0.9.0",
  "description": "React Portlet",
  "keywords": [],
  "scripts": {
    "serve": "parcel main/html/index.html -d build/debug",
    "build": "parcel build main/html/index.html -d build/release",
    "test": "td"
  "dependencies": {
    "react": "^16.4.1",
    "react-dom": "^16.4.1",
    "@monument/core": "^0.9.0",
    "@monument/react": "^0.9.0"
  "devDependencies": {
    "@types/react": "^16.4.6",
    "@types/react-dom": "^16.0.6",
    "parcel-bundler": "^1.9.7"

CLI command:

$ npm run serve

🤔 Expected Behavior

I think that all modules should accur only once in output bundle.

😯 Current Behavior

Currenly some classes are duplicated in output bundle.

💁 Possible Solution

I think root of the problem is symlink structure created by Lerna.

🔦 Context

In project I don’t use code splitting yet.
At some point of time with help of logging I’ve found that some classes are duplicated in output bundle.

💻 Code Sample

In my case module with class “Class” is duplicated as well as probably some others.

🌍 Your Environment

Software Version(s)
Parcel 1.9.7
Node 10.5.0
npm 6.1.0
Lerna 2.11.0
Operating System Windows 10, Ubuntu

4 thoughts on “Duplicated modules in output file

  1. Possible problem is symlinks structure created by Lerna. Output javascript bundle includes same classes but under different file paths. “Unwrapping” symlinks may help in this situation. I mean paths should be pre-processed before registering a chunk to use real file path as chunk ID.

    For example all these paths points to the same file


    but <root>/packages/react/node_modules/@monument/core is symlink that points to <root>/packages/core not a directory itself.

  2. @DeMoorJasper , this bug is really blocker. Will you try to fix it in nearest future? It’s one of core features (resolving file paths) and it does not work properly. I can give more information about use-case if needed.

  3. Now the problem is, if I also include the same file in my other module, the path will be this: ~/main_folder/project/node_modules/module_i_made/lib/much_code1.ts

    We do take the realpath in Parcel 2. Or at least will do that once #5508 is merged