Also, depending on the VM implementation, it might run into issues if you use the same iterator-function with many different callbacks, if there's a limit to how many different values for the callback argument it specializes; don't know what exactly the limits or effects are, but in some simple testing, both Node/V8 and FF/SpiderMonkey slow down on a callback-based-iterator bench if before the main bench the "iterator" was used with multiple different callbacks (whereas the inverse of a single loop iterating through many different iterator types is probably quite a bit more rare).

    myIterator(value => {
        total += value;
    });

I think early Rust even supported the internal iterator style but they abandoned it because IIRC they found external iterations more performant, which is the exact opposite case here.