Deno.SeekerSync

Seek sets the offset for the next readSync() or writeSync() to offset, interpreted according to whence: Start means relative to the start of the file, Current means relative to the current offset, and End means relative to the end.

Seeking to an offset before the start of the file is an error. Seeking to any positive offset is legal, but the behavior of subsequent I/O operations on the underlying object is implementation-dependent.