How to get the user id, username, nick when mentioned by another user

module.exports = {

    callback: async (m) => {
        
        let user = m.member.nickname;
        let mentionedUser = m.mentions.members.first();

        if ( mentionedUser === undefined) {
            m.channel.send("You need to mention someone!")
            return;
        }  
        m.channel.send(`${user} mentioned ${m.mentions.members.first()}`) //test      
    },
};