Gtk.TextIter.prototype.forward_line

function forward_line():Boolean {
    // Gjs wrapper for gtk_text_iter_forward_line()
}

Moves iter to the start of the next line. If the iter is already on the last line of the buffer, moves the iter to the end of the current line. If after the operation, the iter is at the end of the buffer and not dereferencable, returns false. Otherwise, returns true.