Find out which reactions were added and removed in a message_reaction update. This method looks at ctx.messageReaction and computes the difference between the old reaction and the new reaction. It also groups the reactions by emoji reactions and custom emoji reactions. For example, the resulting object could look like this:

{
  emoji: ['👍', '🎉']
  emojiAdded: ['🎉'],
  emojiKept: ['👍'],
  emojiRemoved: [],
  customEmoji: [],
  customEmojiAdded: [],
  customEmojiKept: [],
  customEmojiRemoved: ['id0123'],
}

In the above example, a tada reaction was added by the user, and a custom emoji reaction with the custom emoji 'id0123' was removed in the same update. The user had already reacted with a thumbs up reaction, which they left unchanged. As a result, the current reaction by the user is thumbs up and tada. Note that the current reaction (both emoji and custom emoji in one list) can also be obtained from ctx.messageReaction.new_reaction.

Remember that reaction updates only include information about the reaction of a specific user. The respective message may have many more reactions by other people which will not be included in this update.