UglifyJs Syntax Error fails `npm run build` but not `npm start`

Can you reproduce the problem with latest npm?

Yes.

Description

One of my npm modules causes the production (npm run build) builds to fail with an UglifyJs syntax error. However, I am able to run the app with npm start without any errors or problems.

Expected behavior

Should be able to build production build if development build is working.

Actual behavior

When running npm run build:

Creating an optimized production build...
Failed to compile.

static/js/main.455932b3.js from UglifyJs
SyntaxError: Unexpected token: operator (>) [./~/evolutionary/select1.js:5,0]

Environment

Run these commands in the project folder and fill in their results:

1. npm ls react-scripts (if you haven’t ejected): react-scripts@0.7.0
2. node -v: v6.9.0
3. npm -v: v3.10.9

Then, specify:

1. Operating system: Mac OS X Sierra
2. Browser and version: N/A

Reproducible Demo

1. Generate a new project with create-react-app
2. Run npm install evolutionary
3. Put import 'evolutionary' at the top of index.js
4. Run npm start. Confirm that app loads in browser w/ no errors.
5. Run npm run build. Error appears

I’ve never used webpack, but from my experience with browserify I would assume that ES6 syntax in dependencies would be handled just as fine as my app code.

[cory-baker]

is there no solution to this???

[gre]

It would be neat if create-react-app would support ES6 deps. there are a lot of dependencies I’m relying on (especially around cryptocurrencies/ethereum libs, that are primarly written for Node, and Node does support ES6 now!) that currently publish ES6 code (basically just code with let and arrow functions, nothing fancy) and i’m stuck by not being able to build my project.

Only way I have right now is to eject 😭everything was working smoothly except this. context: I don’t really want to eject because I’m actually writting a starter kit for writing ethereum apps (create-dapp).