const fd = new FormData()
fd.append('x', '1')
[...fd.keys()] // β ['x']
[...fd.values()] // β ['1']keys() and values() return iterators over the FormData field names and values.
values() returns an iterator over all the values in the FormData.
Challenge: Append 'a' -> '1' and verify Array.from(fd.values()) equals ['1'].