widget creation how to

https://docs.mendix.com/howto/extensibility/create-a-pluggable-widget-one#3-3-adding-the-attribute trying to follow the above how to facing the below issue on npm run dev npm run dev npm ERR! Missing script: "dev" npm ERR! npm ERR! To see a list of scripts, run: npm ERR!   npm run Indeed there is no dev script in package.json    I followed all the steps up to this. please guide me to direction thanks in advance  
1 answers

got the solution 

"pluggable-widgets-tools start:web"

 add the above line in scripts of package.json


edit 1

after following all the steps this is the end result not a positive please correct me where this went wrong or some thing wrong on” How-to “ it self