Discord.js - ReferenceError：成员未定义

Question

I am having issues with this, i am trying to add a role called Simon Says Player, can anyone help??

bot.on('message', message => {

    let args = message.content.substring(PREFIX.length).split(" ");

    switch (args[0]) {
        case 'join':

            let person = message.guild.member

            if (!person) {
                return message.reply('Couldn`t find the user!');
            }

            let mainRole = (role => role.name === "Simon Says Player");

            member.addRole(mainRole.id);

            message.channel.send('Successfully Entered The Game!!')

            break;
    }
})

Answer 1

Try message.member.addRole(mainRole.id) instead of member.addRole(mainRole.id)

This should work in your example:

    switch (args[0]) {
        case 'join':

                let person = message.member

                if (!person) {
                    return message.reply('Couldn`t find the user!');
                }

                let mainRole = message.guild.roles.cache.find(role => role.name === "Simon Says Player");
                message.member.roles.add(mainRole);


                message.channel.send('Successfully Entered The Game!!')

            break;
    }

Answer 2

member is in fact undefined , you did not state the intended function but from what I can see you're trying to give a role to the member that sent the join command.

bot.on('message', message => {

  let args = message.content.substring(PREFIX.length).split(" ");

  switch (args[0]) {
    case 'join':

      let person = message.guild.member

      if (!person) {
        return message.reply('Couldn`t find the user!');
      }

      let mainRole = message.guild.roles.cache.find(role => role.name === "Simon Says Player");

      message.member.roles.add(mainRole.id);

      message.channel.send('Successfully Entered The Game!!')

      break;
  }
})