创建Discord Bot：ReferenceError：消息未定义

I have been working on creating a private Discord Bot and I've gotten pretty far with it as of now. There's just 1 issue so far, and I fear more in the future. I am trying to implement an economy system (money system) going off of a video tutorial (https://www.youtube.com/watch?v=Aw4b2VN1KW8) and I am coming across the same error. I have an idea as to what the issue is, but I am unsure of what to do to fix it and how. Below, is my existing index.js code as of now. (5/17/20) I am also using Visual studio code.

const Discord = require('discord.js');
const bot = new Discord.Client();
const fs = require('fs');


let userData = JSON.parse(fs.readFileSync('./Storage/userData.json', 'utf8'));

if (!userData[message.author.id + message.guild.id]) userData[message.author.id + message.guild.id] = {}
if (!userData[message.author.id + message.guild.id].money) userData[message.author.id + message.guild.id].money = 500;

fs.writeFile('Storage/userData.json', JSON.stringify(userData), (err) => {
    if (err) console.error(err);
})

const token = 'my token';

const PREFIX = '+';

bot.on('ready', () =>{
   console.log('This bot is now online.');
   bot.user.setActivity('Mixing drinks');
})

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

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

    switch(args[0]){
        case 'badtouch':
            message.channel.send('*pfffft* a bad touch...')
            break;  
        case 'website':
            message.channel.send('https://va11halla.fandom.com/wiki/VA-11_HALL-A_Wikia')
            break;
        case 'info':
            if(args[1] === 'description'){
                message.channel.send('Stuck here behind this screen in the "lovely" Glitch City, I mix drinks and change lives. Just be sure you have enough money to pay for drinks...');
            }else{
                message.channel.send('That is not a valid command')
            }
            break;
        case 'clear':
            if(!args[1]) return message.reply('There is an error')
            message.channel.bulkDelete(args[1]);
            break;
        case 'random':
            message.channel.send('I wonder if I left enough food at home for Fore... For fore, For four?')
            break;  
        case 'shareabeer':
            message.reply('Cheers. :beers:');
            break;
        case 'commands':
            const attachment = new MessageAttachment('./command list.txt')
            message.author.send(message.author, attachment);
            break;
        case 'aboutme':
            message.reply('My name is Jill, and __NO__, you cannot know my full name. I am alergic to shrimp, I do not mind spicy foods, however I do not really prefer it. A little after graduation and other *events*, I decided to become a bartender.')
            break;
        case 'kira':
            message.channel.send('MIKI!')
            break;
        case 'jules':
             message.reply('Call me Jules and I will make sure every time you sit, you will hear the *cling* of the shaker.')
             break;

    }
})

bot.login(token);

下面是我添加到index.js代码中并开始收到此错误的内容：ReferenceError：消息未定义。如果（！userData [message.author.id + message.guild.id]）userData [message.author.id + message.guild.id] = {}

ReferenceError：消息未定义     在Object。<匿名>

在向其添加这一小节之前，我的机器人工作正常，但尝试启动该机器人时会收到相同的ReferreceError。

let userData = JSON.parse(fs.readFileSync('./Storage/userData.json', 'utf8'));

if (!userData[message.author.id + message.guild.id]) userData[message.author.id + message.guild.id] = {}
if (!userData[message.author.id + message.guild.id].money) userData[message.author.id + message.guild.id].money = 500;

fs.writeFile('Storage/userData.json', JSON.stringify(userData), (err) => {
    if (err) console.error(err);
})

如果我没有记错的话，我必须定义“消息”，但是我该如何以及在哪里做呢？如果可以，是否可以提供示例？

非常感谢。