'cross-env' is not recognized as an internal or external command

I came to this error when i had already websocket installed and npm run watch was running and i was trying to install php artisan ui vue --auth

Now to solve this error stop npm run watch if it was running and write in console: 

npm cache clear --force

then, 

npm install

and,

npm run dev

This should work if it doesn't then run 

npm cache clear --force

npm install cross-env

npm install 
npm run dev