I have cloned a existing block and now i am are trying to add my custom fields in form component in front end http://prntscr.com/lzlaol .So, for that i checked in documentation and in forum previous question related to this topic i found to make changes and to reflect them on front i need to create a build and i just for testing add a console.log() in assets/js/modules/builderstyleeditor.js file and try to run "npm run build" on my server and the result is http://prntscr.com/lzlclu. command removed the previous build folder but not created a new one.

Same i have tried by set the ENVIRONMENT variable to "development" in index.php and run command npm start and result is http://prntscr.com/lzle3h