How to define a DOSKEY alias for multiple commands?
The command separator for DOSKEY is $T
For your example:
DOSKEY nss=npm start $T npm run serve
Try writing it as a batch file and then calling the batch file use the DOSKEY command
REM do_npm.batnpm startnpm run serve
Then, run the DOSKEY command
DOSKEY npm=do_npm.bat
See if that works for you