Cleanup Jest config

[ianschmitz]

General cleanup after the Jest 24 PR.

This also includes jsdom@14 via https://www.npmjs.com/package/jest-environment-jsdom-fourteen. Since we have a node >= 8.10 requirement, we are able to use the latest version of jsdom which includes additional implementations of browser APIs such as MutationObserver (which we had an issue filed for over at #6617).

/cc @SimenB. Is there more you recommend we do to cleanup our Jest config for TypeScript?

[SimenB]

WRT TypeScript, I think you're good (Jest by default finds ts and tsx, but you have more opinionated paths on top of its defaults). Other things I noticed though:

create-react-app/packages/react-scripts/scripts/utils/createJestConfig.js

Lines 27 to 31 in b0cbf2c

	setupFiles: [
	isEjecting
	? 'react-app-polyfill/jsdom'
	: require.resolve('react-app-polyfill/jsdom'),
	],

Ditch isEjecting condition - we want require.resolve no matter what and not rely on the package manager hoisting things

create-react-app/packages/react-scripts/scripts/utils/createJestConfig.js

Line 38 in b0cbf2c

testEnvironment: 'jsdom',

I'd prefer require.resolve('jest-environment-jsdom'); and add a dependency on it, but Jest has dependencies on jest-environment-{jsdom,node} so it'll be able to resolve these on its own. So you might not want that, although that means jest might load some other version of the env than CRA expects. Not sure if that's a feature or not

create-react-app/packages/react-scripts/scripts/utils/createJestConfig.js

Line 42 in b0cbf2c

? '<rootDir>/node_modules/babel-jest'

require.resolve('babel-jest'); instead of making assumptions about where in node_modules it resides

create-react-app/packages/react-scripts/scripts/utils/createJestConfig.js

Lines 53 to 56 in b0cbf2c

	moduleNameMapper: {
	'^react-native$': 'react-native-web',
	'^.+\\.module\\.(css|sass|scss)$': 'identity-obj-proxy',
	},

require.resolve at least on identity-obj-proxy. Maybe not RNW as that's up to the user and it should always be in the top level so Jest should be able to resolve irregardless of package manager hoisting

[ianschmitz]

Thanks a ton @SimenB. Great feedback. I'll incorporate your recommendations shortly.

Would you recommend using using https://github.com/theneva/jest-environment-jsdom-thirteen for testEnvironment as mentioned in the Jest docs? I imagine it would help with issues like #6617 since they've recently added support for MutationObserver. We have a node 8 requirement for CRA now anyways so I can't really see a downside?

[SimenB]

Would you recommend using using theneva/jest-environment-jsdom-thirteen for testEnvironment as mentioned in the Jest docs?

JSDOM 14 has come out, so I'd probably jump straight to that (not sure if anyone's released a jest environment for it yet, though). Good call 🙂

[ianschmitz]

JSDOM 14 has come out, so I'd probably jump straight to that (not sure if anyone's released a jest environment for it yet, though). Good call 🙂

Working on it 😉

https://github.com/ianschmitz/jest-environment-jsdom-fourteen

[SimenB]

You might wanna update to jest 24.6, it has a few perf improvements