Not to put words in his mouth, but the point I think japhy
(right?) was trying to make was that, if the reason you're
writing to the beginning of the file is that you think that
there's where you should store the most "recent"
information, then there's really no point.
Just keep your
file in chronological order (oldest at beginning, newest
at end) and, when you're reading the file into memory,
use unshift rather than push so that the newest data
ends up at the beginning of the array.
Which definitely makes sense, and makes the problem quite
a lot less complicated, if that's the reason the op
wanted to write to the beginning of the file.