Function iter_for_each 

pub fn iter_for_each(
    src: &Value,
    f: impl FnMut(Value, usize) -> Result<(), String>,
) -> Result<(), String>

Drive an iterator object (one with a .next() returning {value, done}) to exhaustion. Step src’s iterator, handing each value to f, and CLOSE the iterator if f exits abruptly (7.4.9 IteratorClose).

The difference from iter_all + a loop is that this never materializes the whole sequence: Array.from(infinite, mapFn) where mapFn throws has to stop at the first call, and draining first means it never gets there at all.