Many users have had trouble with not seeing changes in the browser on a custom dashboard even after saving your JS/HTML files.
If you have set up your file structure correctly it may be that you need to clear your browsers cache and do a hard refresh. This is a common issue is web development. Here are some shortcuts to do so:
If you are using google chrome you can have you developer tools open and check the box that says 'Disable Cache' under the network tab. Now when you refresh the page with the dev tools open it will load a fresh copy of all source files. Ctrl+F5 is reported to work as well.
If you are using Safari you can do a cmd+opt+e to clear cache before hitting cmd+r to reload the page and it will do the same.