I recently discovered that c:/Users/username/AppData/Local/AppName/Cache
contained over 100K cache files.
I read up a bit and saw that the gui.App.cl
It is now 2019 and clearCache() does function by adding the following:
var gui = require('nw.gui');
gui.App.clearCache();
or
nw.App.clearCache();
This will clear the HTTP cache in memory and the one on disk whatever your platform. I have tested it on Mac OS but maybe there can be user permission issues on Linux.
On MacOS, you can check in real time that the cache folder is emptied at
Mac HD ▸ Users ▸ youruser ▸ Library ▸ Caches ▸ yourapp ▸ Default