Bangle.js program being read partially and giving errors

Unfortunately, the errors produced are rather different every time the code changes. It does seem to be happening in the same module (we're using Webpack), and that particular module does contain a recursive function along the lines of:

class C {
    ...
    f() {
        ...
        somePromise.then(() => {
            ...
            f()
        })
    }
    ....
}

However, the errors occur at other functions, some only ever called before said recursive function, and some always called after it. One possible commonality (I've only just noticed so I haven't been able to verify just yet) is that they all seem to use promises. Then again, it might simply be because that particular class uses promises in a few different places.

By the way, after trying to follow the above instruction to do storage compaction, I tried to reset (long press BTN3), and got the following exception:

>require('Storage').compact()
=undefined
>
Uncaught ReferenceError: "attery" is not defined
 at line 1 col 3
W+CHARP;var d=new Date();g.reset();g.setFont("6x8");g.setF­ontAlign...
        ^
in function called from system
 at line 1 col 1
attery()*(s-12)/100,y+17);g.setColor(-1)­;}Bangle.on('chargin...
^
in function called from system

and when I tried to run the app it turned out the file was corrupted (with sequences of \ff at two places in the file). Is this to be expected? I repeated the steps and it the file was not corrupted the second time, though I got the same exception from long pressing BTN3.