我想檢查是否agrs[1]是會員名。我目前使用的代碼：const Discord = require ('discord.js')const client = new Discord.Client() const PREFIX = "!"; client.on('ready', () => {    console.log('connect as ' + client.user.tag)    let guild = client.guilds.get('636639114787291137')})client.on('message', message =>{    let agrs = message.content.substring(PREFIX.length).split(" ");    switch (agrs[0]){        case 'teammate':            if (!agrs[1]) {                return message.reply("enter a member after !teammate")            }            else {                message.reply(agrs[1])             }        break;    }})client.login("xxx")