[BUG] Unable to resolve dependency in Create React App Typescript template

[strican]

Current Behavior:

Based off the feedback in #2000, I'm filing a unique bug on this. In an empty React Applicaiton created with the create-react-app Typescript template, npm install fails with the following:

$ npm install
npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR! 
npm ERR! Found: [email protected]
npm ERR! node_modules/typescript
npm ERR!   typescript@"^4.0.3" from the root project
npm ERR! 
npm ERR! Could not resolve dependency:
npm ERR! peerOptional typescript@"^3.2.1" from [email protected]
npm ERR! node_modules/react-scripts
npm ERR!   react-scripts@"4.0.0" from the root project
npm ERR! 
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.

Expected Behavior:

npm install should succeed

Steps To Reproduce:

npx create-react-app myapp --template typescript
cd myapp
rm -rf node_modules
npm install

Environment:

• OS: MacOS 10.15.6
• Node: 15.1.0
• npm: 7.0.8

[ljharb]

This version of react-scripts requires typescript 3, and you’re using typescript 4. To make your dep graph valid, you’ll have to downgrade typescript, or upgrade to a version of react-scripts that allows typescript 4, if it exists.

[strican]

Is this a bug with Create React App then? The install works with Yarn though. Is NPM being stricter about dependencies than other package managers?

[ljharb]

No, it’s a bug with your package.json, since that’s what declares typescript. However, if CRA is generating that, then yes, it’s a bug in CRA.

npm 7 properly checks peer deps on install (altho it unfortunately doesn’t fail by default when there’s a peer dep issue like this), and i don’t believe any other npm package CLIs do.

[strican]

Thanks for the explanation. Looks like this was filed as facebook/create-react-app#9995.

[ljharb]

facebook/create-react-app#9964 seems like it will fix it, once merged and released. Closing this in favor of the linked issue and PR.

[lalberto8085]

Hello I know it's been a while, what version was this fixed on?

[ljharb]

@lalberto8085 no version of npm; if you click on the CRA PR, and on the commit that merged it, you'll see it's not released there yet.

[SurajJadhav7]

This issue is still present.

My Environments:

OS: MacOS 11.2.3
Node: 15.12.0
npm: 7.6.3

I was able to resolve it by downgrading typescript version in package.json

"devDependencies": {
    "@babel/runtime": "7.13.8",
    "typescript": "3.2.1"
  },