Question

which grunt plug-in would be of use if you would like to monitor set of .js files and take any appropriate actions if any changes happens to them?

Answer 1

Sass file can be processed by a tool named Grunt this also helps to process various other files like image,java script.

Grunt- contrib -watch plugin can be used  to monitor .js files and thus can take various actions if any sort of changes are done to them and it is very easy to set up.