Saving modules and using saved functions?

It sounds like as @Wilberforce says just saving the code will do what you want... Here's a good start: http://www.espruino.com/Saving

However if you simply type var StepperMotor = require("StepperMotor") into the right-hand side of the IDE, choose 'even after reset' for 'Save on Send' from the IDE options, upload, and then turn 'save on send' to off again, you can then write code and type save() and it'll save, and can even use reset() to reset state, but you'll always have access to the saved code you saved originally.