SystemJS module loader uses XHR to load module files from the server. This means that it is subject to caching issues.
In order to prevent caching during development most developer do one of the following:
1. Open browser’s DevTools and disable the cache
2.Configure the local web server so each module is sent back to the browser with the appropriate cache buster headers
When dealing with large scale SPA application this behavior might be too expensive. Assuming you have SPA with hundreds of files (quite common these days), refreshing the browser while cache is disabled is time consuming.
See more details and sample at the Github repository.