Answers for "discord.js message on member join"

send a message when a bot joins your server discord.js

client.on('guildCreate', guild => {
  guild.systemChannel.send(`Hello, I'm LMAOBOT. Thanks for inviting me, here are a list of all my commands! :alien:`)
});

discord.js message on member add

client.on('guildMemberAdd', member => {
    member.send("Welcome!");
});