Check out example codes for "npm 'cross-env' is not recognized as an internal or external command". It will help you in understanding the concepts better.

Code Example 1

npm install -global cross-env
npm install --no-bin-links

Code Example 2

First run:

rm -rf node_modules
rm package-lock.json yarn.lock
npm cache clear --force

Then run the command:

npm install cross-env

npm install 

and then you can also run:

npm run dev

Learn ReactJs, React Native from akashmittal.com