  We present the first IRIS Mg II slit-raster spectra that fully capture the
genesis and coronal-jet-generating eruption of a central-disk solar
minifilament. The minifilament arose in a negative-magnetic-polarity coronal
hole. The Mg II spectroheliograms verify that the minifilament plasma
temperature is chromospheric. The Mg II spectra show that the erupting
minifilament's plasma has blueshifted upflow in the jet spire's onset and
simultaneous redshifted downflow at the location of the compact jet bright
point (JBP). From the Mg II spectra together with AIA EUV images and HMI
magnetograms, we find: (i) the minifilament forms above a flux cancelation
neutral line at an edge of a negative-polarity network flux clump; (ii) during
the minifilament's fast-eruption onset and jet-spire onset, the JBP begins
brightening over the flux-cancelation neutral line. From IRIS2 inversion of the
Mg II spectra, the JBP's Mg II bright plasma has electron density, temperature,
and downward (red-shift) Doppler speed of 1012 cm^-3, 6000 K, and 10 kms,
respectively, and the growing spire shows clockwise spin. We speculate: (i)
during the slow rise of the erupting minifilament-carrying twisted flux rope,
the top of the erupting flux-rope loop, by writhing, makes its field direction
opposite that of encountered ambient far-reaching field; (ii) the erupting kink
then can reconnect with the far-reaching field to make the spire and reconnect
internally to make the JBP. We conclude that this coronal jet is normal in that
magnetic flux cancelation builds a minifilament-carrying twisted flux rope and
triggers the JBP-generating and jet-spire-generating eruption of the flux rope.
