The feast of St. John the Apostle and Evangelist is a Double of the Second Class with, since the reform of 1911-13, a simple Octave. Before that reform the feast had a common Octave. The liturgical colour of the feast is white. The feast completely displaces the Sunday within the Octave of the Nativity.
At Mattins the invitatory is Regem Apostolorum Dominum, Venite adoremus and the Office hymn is Aeterna Christi munera, sung with the Doxology of the Incarnation. In the first nocturn the antiphons In omnem terram etc are sung, doubled, with psalms 18, 33 & 44. The lessons are the Incipit of the former Epistle of St. John. The responsories are proper to the feast. In the second nocturn the antiphons Principes populorum etc are sung, doubled, with psalms 46, 60 & 63 and the lessons are from the writings of St. Jerome. In the third nocturn the antiphons Exaltabuntur etc are sung, doubled, with psalms 74, 96 & 98. The homily on St. John's Gospel is from St. Augustine. The Te Deum is sung. At Lauds the antiphons Valde honorandus est etc are sung, doubled, with the Dominical psalms (92, 99, 62, Benedicite & 148). The Office hymn is Exsultet orbis gaudiis sung with the Doxology of the Incarnation. The antiphon on the Benedictus, Iste est Joannes etc., is proper to the feast. After the collect of the feast a commemoration is sung of the Octave of the Nativity.
At the Hours the hymns are sung with the Doxology of the Incarnation. At Prime the antiphon Valde honorandus est is sung with the festal psalms (53, 118i & 118ii) and the lectio brevis is In medio Ecclesiae. The antiphons from Lauds are sung in due order at the other Horae Minores.
Mass is sung after Terce. The Gloria is sung, the second collect is of the Octave of the Nativity. The Creed is sung, the preface and communicantes are of the Nativity.
Vespers are of the Nativity but from the chapter of St. John. The Office hymn, Exsultet orbis gaudiis, is sung with the Doxology of the Incarnation. Commemorations are sung of tomorrow's feast of the Holy Innocents and of the Octave of the Nativity.
At Compline the Dominical psalms are sung and the Dominical preces are omitted.
Following the 'liturgical books of 1962' today is the Sunday within the Octave of the Nativity (although no commemoration of the Octave is made). Mattins (of the Sunday) is cut down to a single nocturn of three lessons. The Doxology in honour of the Incarnation is omitted in the singing of the Office hymns of the Little Hours. At the Little Hours the antiphons and psalms are taken from the psalter for Sunday, not from the feast. At Prime the lectio brevis is of the season. St. John gets commemorated at Lauds and in said Masses. At other Masses there is a single collect. At Vespers no commemoration is made of the Holy Innocents nor of St. John or the Octave of the Nativity.
Miniature of St. John from Wikipedia.