Site caching is a browser feature. Found a link to describe, how to do it, and only for a specific site.
And a little note from myself, I did notice that "jump" sound is played whenever button pressed, but if I spam it mid-jump, trying to get over croud in spa, it might be a little annoying. So a simple condition check "play sound if character grounded" would be great (or "play sound if char vertical speed is zero,", pick whatever suits you)