What version of JS does Espruno implement? (ES5/ES6)

Do arrow functions save more memory than normal functions?

Yes and no - they use less characters so that's less bytes for the actual code. However when they're defined they often use 2 more variables since they have to store this for each function.

If you're using the pretokenise flag then the function keyword gets squished down so a lot of that benefit disappears.

The actual memory used should be the same on all platforms though.