the sound of the laughter of someone who is laughing (see Molina) (an onomatopoetic word)
Alonso de Molina:
ha ha ha. a a a, del que se rie. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 30r. col. 1. Thanks to Joe Campbell for providing the transcription.