discord.js/src/client/actions/UserUpdate.js

const Action = require('./Action');
const { Events } = require('../../util/Constants');

class UserUpdateAction extends Action {
  handle(data) {
    const client = this.client;

    if (client.user) {
      if (client.user.equals(data)) {
        return {
          old: client.user,
          updated: client.user,
        };
      }

      const oldUser = client.user._update(data);
      client.emit(Events.USER_UPDATE, oldUser, client.user);
      return {
        old: oldUser,
        updated: client.user,
      };
    }

    return {
      old: null,
      updated: null,
    };
  }
}

module.exports = UserUpdateAction;