John's gospel is independent of the other three. It was probably written in the late 90s C.E. In itself it is rather complicated and the gospel that we have today as "John's Gospel" may be the result of three or four redactions. It is possible that there was an initial version of John's gospel which circulated. This was probably redacted and this revised version circulated for a while. This then was redacted and a third version circulated for a while. Finally this third version was redacted and this is what has come down to us today as John's gospel.