This is due to caching by the web browser, which is normal behaviour to prevent unnecessary reloading of the .js file - which can be awkward when performing development. As this is normal browser behaviour you may find information on how to suppress the cache and force a reload by Googling these terms.
The caches are only cleared automatically by web browsers when you close all the instances of the browser, which will include closing Sense. For occasional changes to the extensions, that may be OK, but it is inconvenient at least.
Although I am not sure whether these will work with the browser in QS desktop...
Two other way of clearing Chrome cache :
a) Hit Ctrl+Shift+Delete (windows) and you'll get a opup window with an option to clear the cahe.
b) If you start chrom Dev Tools on a particular tab, a "long" press (one or two seconds) on the reload icon will pop up some options. The third option will force cache clear before reload.