Resolving Create React App’s “Uncaught ReferenceError: process is not defined”

Charles Stover
1 min readDec 31, 2021

A recent change to Create React App, or more specifically react-scripts, has caused hot reloading to throw an error: Uncaught ReferenceError: process is not defined. This is due to its dependency, react-error-overlay, being referenced as ^6.0.9 while react-error-overlay’s latest patch version 6.0.10 is a breaking change. As a result, your installation likely uses 6.0.10 when it needs 6.0.9. To fix this, you unfortunately need to Frankenstein your yarn.lock file.

Find your react-error-overlay@^6.0.9 entry, which should have its resolution [incorrectly]set to 6.0.10:

"react-error-overlay@npm:^6.0.9":
version: 6.0.10
resolution: "react-error-overlay@npm:6.0.10"
checksum: e7384f086a0162eecac8e081fe3c79b32f4ac8690c56bde35ab6b6380d10e6c8375bbb689a450902b6615261fcf6c95ea016fc0b200934667089ca83536bc4a7
languageName: node
linkType: hard

Replace this entry with the following, which resolves to 6.0.9:

"react-error-overlay@npm:^6.0.9":
version: 6.0.9
resolution: "react-error-overlay@npm:6.0.9"
checksum: 695853bc885e798008a00c10d8d94e5ac91626e8130802fea37345f9c037f41b80104345db2ee87f225feb4a4ef71b0df572b17c378a6d397b6815f6d4a84293
languageName: node
linkType: hard

Once saved, run yarn install again to pull the correct version into your node_modules and/or .yarn/cache directory. Your React application should now hot reload correctly.

To track this error in an official capacity, you can view this issue on GitHub.

Charles Stover

Staff front end engineer | Tech lead | Architect | charlesstover.com