The full error is

if(command.permissions.length){
                       ^
TypeError: Cannot read properties of undefined (reading 'length')

There is a Stack Overflow answer that is exactly like my code because I am also going off the CodeLyon's tutorials but I do not understand the answer that they have provided.

My code is:

const fs = require('fs')
const commandFiles = fs.readdirSync('./commands/').filter(file => file.endsWith('.js'));

require('dotenv').config();
//create cooldowns map
const cooldowns = new Map();
module.exports = (Discord, client, message) => {
    const prefix = process.env.PREFIX;
    if (!message.content.startsWith(prefix) || message.author.bot) return;

    const args = message.content.slice(prefix.length).split(/  /)
    const cmd = args.shift().toLowerCase();

    const command = client.commands.get(cmd) || client.commands.find(a => a.aliases && a.aliases.includes(cmd));

    const validPermissions = [
        "CREATE_INSTANT_INVITE",
        "KICK_MEMBERS",
        "BAN_MEMBERS",
        "ADMINISTRATOR",
        "MANAGE_CHANNELS",
        "MANAGE_GUILD",
        "ADD_REACTIONS",
        "VIEW_AUDIT_LOG",
        "PRIORITY_SPEAKER",
        "STREAM",
        "VIEW_CHANNEL",
        "SEND_MESSAGES",
        "SEND_TTS_MESSAGES",
        "MANAGE_MESSAGES",
        "EMBED_LINKS",
        "ATTACH_FILES",
        "READ_MESSAGE_HISTORY",
        "MENTION_EVERYONE",
        "USE_EXTERNAL_EMOJIS",
        "VIEW_GUILD_INSIGHTS",
        "CONNECT",
        "SPEAK",
        "MUTE_MEMBERS",
        "DEAFEN_MEMBERS",
        "MOVE_MEMBERS",
        "USE_VAD",
        "CHANGE_NICKNAME",
        "MANAGE_NICKNAMES",
        "MANAGE_ROLES",
        "MANAGE_WEBHOOKS",
        "MANAGE_EMOJIS",
      ]
    
    
    if(command.permissions.length){
        let invalidPerms = []
        for(const perm of command.permissions){
            if(!validPermissions.includes(perm)){
                return console.log(`Invalid Permissions ${perm}`);
            }
            if(!message.member.hasPermission(perm)){
            invalidPerms.push(perm);
            }
        }
        if (invalidPerms.length){
          return message.channel.send(`❌| Missing Permissions: \`${invalidPerms}\``);
        }
    }

    //If cooldowns map doesn't have a command.name key then create one.
    try{
        if(!cooldowns.has(command.name)){
            cooldowns.set(command.name, new Discord.Collection());
        }
    } catch (err) {
        return message.reply("❌|I did not find that command");
    }

    const current_time = Date.now();
    const time_stamps = cooldowns.get(command.name);
    const cooldown_amount = (command.cooldown) * 1000;

    //If time_stamps has a key with the author's id then check the expiration time to send a message to a user.
    if(time_stamps.has(message.author.id)){
        const expiration_time = time_stamps.get(message.author.id)   cooldown_amount;

        if(current_time < expiration_time){
            const time_left = (expiration_time - current_time) / 1000;

            return message.reply(`❌|Please wait ${time_left.toFixed(1)} more seconds before using ${command.name}`);
        }
    }

    //If the author's id is not in time_stamps then add them with the current time.
    time_stamps.set(message.author.id, current_time);
    //Delete the user's id once the cooldown is over.
    setTimeout(() => time_stamps.delete(message.author.id), cooldown_amount);

    try{
        command.execute(message, args, cmd, client, Discord);
    } catch (err){
        message.reply("❌| There was an error trying to execute this command");
        console.log(err);
    }

}

CodePudding user response：

The error means that in at least one of your command files, the exported object has no permissions array, or permissions is not an array.

It's probably a good idea to check if command.permission exists and if not, just skip that part. The optional chaining operator (?) will work fine:

if (command.permissions?.length) { 
  // ...