Allow to disable regenerator-runtime

[z-vr]

With the current configuration, async is transpiled into generators. If I have an error in an async function, my VS Code with chrome-debugger extension loads bundle.js and jumps to _asyncToGenerator ... catch (error) { reject(error); return; } ... there which is quite laggy.

Exception has occurred: Error
Error
    at _callee3$ (/Users/anton/Work/abc/src/containers/src.js:125:1)
    at tryCatch (/Users/anton/Work/abc/node_modules/regenerator-runtime/runtime.js:62:1)
    at Generator.invoke [as _invoke] (/Users/anton/Work/campaign-design/node_modules/regenerator-runtime/runtime.js:296:1)
    at Generator.prototype.(anonymous function) [as next] (/Users/anton/Work/abc/node_modules/regenerator-runtime/runtime.js:114:1)
    at step (http://localhost:3000/static/js/bundle.js:93038:191)
    at http://localhost:3000/static/js/bundle.js:93038:361
    at <anonymous>

Since async/await is widely supported, and during development, it's desirable to disable the regenrator runtime.

For anyone interested, you have to update node_modules/babel-preset-react-app/index.js and add

        exclude: [
            'transform-regenerator',
            'transform-async-to-generator',
          ],

at line 113 (babel-preset-env config), then do yarn --force.

This also means I can't set brakepoints at the lines with await keyword which is pretty annoying.

[Timer]

You can try the 2.x alphas which let you specify target browsers. If you target the latest chrome version, your async functions will remain as-is.

[z-vr]

@Timer if there any more info on how to do that anywhere please?

[Timer]

#3815

[z-vr]

@Timer I know you've closed this, but is it possible to have 2 separate configs for dev and prod? Otherwise it's always required to remove "browserlist" from package.json when building.

[z-vr]

I think I can do

"browserslist": {
  "development": [
    "last 1 Chrome version"
  ]
}

actually
thanks.

[kyeotic]

@z-vr can you explain where that config goes?

[Timer]

@tyrsius when you start an app with react-scripts 2.0, look in your package.json -- you'll find browserslist there.

[kyeotic]

@Timer Ok, I don't think I have that then. I've ejected and Im trying to figure out how to send this option into babel (or preset-env)

[samdesota]

I've been fighting this for hours now, it appears "browserslist": { "development": [ "last 1 Chrome version" ] }
Dosen't do anything on the latest create-react-app on linux. Anybody able to reproduce?

[justingrant]

@mrapogee - Unfortunately the ability to use browsersList to disable regenerator and other polyfills was removed before V2 of CRA was released. Like you, I also wasted a bunch of time before figuring it out that the advice given by @Timer and @z-vr was accurate when they gave it, but it doesn't apply anymore to current CRA2 releases.

If you (like me!) want to see this implemented, @ianschmitz suggested to make #6198 the master issue to track this request. Go there add your votes and ideas!