Regardless of what Espruino device you have, require("Storage").getFree() should work fine.
require("Storage").getFree()
There may be the odd bit of flash left outside storage on some builds, but the vast majority is usually in Storage
@Gordon started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Regardless of what Espruino device you have,
require("Storage").getFree()
should work fine.There may be the odd bit of flash left outside storage on some builds, but the vast majority is usually in Storage