Is there an API for that?
You can use the paths API for that: call overwolf.io.paths.localAppData
and concatenate your extension id and your app version to it:
Overwolf.io.paths.localAppData + "/overwolf/extensions/[your extension id]/[version]"
Where version can be retrieved from the manifest.
Another trick is to use the simpleio plugin to get the paths.
Btw, this way doesnt work if extension is loaded as unpacked while developing. Almost in my case, my app is not in %localappdata%\Overwolf\extensions\etc etc" while testing it.
Thanks for the comment! make sense.
I added this example and note to the new dev site (which is not live yet).