Play audio file when someone joins voice channel - discord.js

Question

I followed some tutorials and got some help, but no matter what I try it keeps showing an error with the playFile. The bot can also play music but the music (through a link) part works fine. So how would I play an audio file that's in the root folder and only when someone joins the voice channel?
bot.on('voiceStateUpdate', (oldMember, newMember) => {
// Here I'm storing the IDs of their voice channels, if available
let oldChannel = oldMember.voiceChannel ? oldMember.voiceChannel.id : null;
let newChannel = newMember.voiceChannel ? newMember.voiceChannel.id : null;
if (oldChannel === newChannel) return; // If there has been no change, exit
// Here I'm getting the bot's channel (bot.voiceChannel does not exist)
let botMember = oldMember.guild.member(bot.user),
botChannel = botMember ? botMember.voiceChannel.id : null;
var server = servers[botMember.guild.id];
// Here I'm getting the channel, just replace VVV this VVV with the channel's ID
let textChannel = oldMember.guild.channels.get('438025505615249408');
if (!textChannel) throw new Error("That channel does not exist.");
// Here I don't need to check if they're the same, since it would've exit before
if (newChannel === botChannel) {
// console.log("A user joined.");
server.dispatcher = botMember.voiceConnection.playFile('./audiofile.mp3');
textChannel.send(newMember.displayName + " joined.");
} else if (oldChannel === botChannel) {
// console.log("A user left.");
textChannel.send(newMember.displayName + " left.");
}
});

Answer 1

Side note: you're using GuildMember.voiceConnection, but that property does not exist. Look a the docs for GuildMember.
The docs for VoiceConnection.playFile() say that the file argument has to be an absolute path (like C:/yourfolder/audio.mp3). To convert a relative path (./audio.mp3) to an absolute one, you need to join the directory (stored in the global variable __dirname) and the relative:
let conn = bot.voiceConnections.get(newMember.guild.id);
if (!conn) throw new Error("The bot is not in a voiceChannel, fix your code.");
let path = __dirname + '/audiofile.mp3';
conn.playFile(path);
Alternatively, you can use the path module (docs).
let path = require('path').join(__dirname, './audiofile.mp3');
conn.playFile(path);