Dev build doesn't include Set polyfill

[Ismael]

React 16 requires Set.
I'm developing for an older browser which does not have Set. In production mode, the project works. In dev mode, I get an Set is undefined error.

I'm importing babel-polyfill at the top of my index.js, but that doesn't work.
I tried importing core-js/es6/set directly and didn't work either.

How can I make sure the dev build includes support for legacy browsers?

Also, maybe you should include Set by default in the polyfills as this is required by React 16?

https://github.com/facebookincubator/create-react-app/blob/master/packages/react-scripts/template/README.md#supported-language-features-and-polyfills

[tharakawj]

Already there is pending PR for this. #3200

[Ismael]

But I did add those two polyfills and dev didn't work, only prod. Is there any reason for the polyfills not loading on dev?

[gaearon]

We don't intend to include a Map, Set, or requestAnimationFrame polyfills with CRA.
You are welcome to add them yourself if you target browsers that require them.

[pridemusvaire]

@Ismael include babel-poly-fill in public/index.html as a script tag, that will solve most of your problems.