[react-is] export individual modules to enable tree-shaking capabilities

[pgarciacamou]

What is the issue

Tree shaking not enabled with react-is.

import * as ReactIs from "react-is";
ReactIs.isValidElementType(<div />); // true

Expected behavior

Allow importing individual modules from the package.

import { isValidElementType } from "react-is";
isElement(<div />); // true

Checklist

• fix bug
• yarn
• yarn test
• yarn test-prod
• yarn prettier
• yarn lint
• yarn flow dom && yarn flow test
• complete the CLA

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[pgarciacamou]

I'm not sure if this line will work, any comments are welcomed.

[jquense]

Hey there thanks for the PR. I'm not sure what you'r trying to accomplish here, export * from ''./src/ReactIs' and explicitly exporting each export should be equivalent. e.g. the export * is shorthand for what you've added here.

[pgarciacamou]

@jquense

What I'm trying to accomplish is to do import { isValidElementType } from "react-is". It doesn't work with this PR made to react-redux reduxjs/react-redux#971

Also, I found an old thread in webpack which I'm unsure if it was ever fixed webpack/webpack#2847

[aweary]

We'd need to add an ESM build to support tree-shaking, per this comment

[pgarciacamou]

@aweary can you point me in the right direction? I'm not sure what ESM means. I'll try to get a PR open.

• Do you mean: https://rollupjs.org/guide/en#es-module-syntax?
• What files should I be taking a look at? react/packages/react-is/npm or react/scripts/rollup?

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[timdorr]

@pgarciacamou ESM = ES Modules = import/export

[pgarciacamou]

Well, I'm totally lost on how to do that in such a big project like React.

I want to believe I've narrow it down to https://github.com/facebook/react/blob/master/scripts/rollup/build.js#L448-L478 but I'm not sure.

There is a related issue maybe: #11503, but I think that is only around the top level API and not the packages.

I'm going to create an issue about react-is.