String.split misbehaves in chrome 51 with canary build

[bdwain]

Can you reproduce the problem with latest npm?

yes

Description

The native string split method seems to no longer work correctly in the console (or my app) when i load my app in production mode (it's fine if i don't minify it). I've tracked this issue down to a specific change in how webpack uses uglify. i filed an uglify issue with a little more detail, but it's still relevant here because it's using those tools.

Expected behavior

In the console:

let str = 'fooBar'
str.split(/(?=[A-Z])/)

> ["foo", "Bar"]

Actual behavior

let str = 'fooBar'
str.split(/(?=[A-Z])/)

> ["fooBar"]

Environment

react-scripts@1.0.0-alpha.e280254d
node: v7.9.0
npm: 4.2.0
yarn (which i'm actually using, not npm): 0.23.3

os: os x sierra
browser: chrome 51 (other versions (back to chrome 30) seem fine)

Reproducible Demo

https://github.com/bdwain/uglify-bug

all you need to do to reproduce is run create-react-app with the canary build of react-scripts, and then npm install (or yarn add) babel polyfill and include it in your entry point. The result of yarn build will then cause the issue. Open a production build of the app (dev mode is fine), then open a console and try to run string split.

[gaearon]

We need to check if manually disabling reduce_vars option fixes it.

[bdwain]

@gaearon i went into the react scripts node_modules folder and changed the uglify webpack plugin to look like this

 new webpack.optimize.UglifyJsPlugin({
  compress: {
    warnings: false,
  },
  output: {
    comments: false,
  },
  sourceMap: true,
  reduce_vars: false //added this
}),

but it still failed.

it happens in my app also (which is not using CRA) no matter what options I try to specify

[gaearon]

It should be inside compress, can you try that?

[bdwain]

ah that fixes it! good catch. is that a bug in that uglify feature then?

[gaearon]

Yes.

[bdwain]

cool thanks for your help!

[gaearon]

Can you confirm my fix works for you?
#2200

[bdwain]

@gaearon is there a way i can install that specific build of react-scripts? it looks like the same fix that worked for me above, but i'm unable to run it to make sure.

it seems like react-scripts isn't its own repo so i couldn't have package.json reference the commit hash.

[gaearon]

You could replace webpack.config.prod.js with this version to verify.

[bdwain]

oh sorry. then yes it works. that's what i did before when i tested. i thought you wanted me to just run your version by installing it without manually changing it.