How should i go about making a memory system for my bot?

This is my command handler, or, is it a command handler?

`

const Discord = require('discord.js');
const client = new Discord.Client();
const prefix = '$'
const sqlite = require('sqlite3').verbose();
client.once('ready', () => {
console.log('Advice Dog is online!');
})
client.on(`message`, async message => { 
let userid = message.author.id;
let uname = message.author.tag
if (message.author.bot)return;
let db = new sqlite.Database('./testdb.db', sqlite.OPEN_READWRITE)
db.run(`CREATE TABLE IF NOT EXISTS data(userid INTEGER NOT NULL, username TEXT NOT NULL)`);
if (msg == ".getdata"){
let query =  `SELECT * FROM data WHERE userid = ?`
db.get(query, [userid], (err, row) => {
if (err) {
console.log(err);
return;
                }
if (row === undefined)  {
let insertdata = db.prepare(`INSERT INTO data VALUES(?,?)`) 
insertdata.run(userid, uname)
insertdata.finalize(); 
db.clost();
return;
            } else {
let userid2 = row.userid;
let word = row.word;
console.log(word)
            }
        });
    }
if (msg.startsWith(".change")) {
let word = msg.slice(8);
db.run(`UPDATE data SET word = ?, WHERE userid = ?`, [word, userid])
console.log("done!")
    }

 });
client.on('message', message => {
if(!message.content.startsWith(prefix) || message.author.bot) return; 
const args = message.content.slice(prefix.length).split(/ + /);
const command = args.shift().toLowerCase();
if(command === 'ping'){
message.channel.send('``pong!``');`

/r/Discord_Bots Thread Parent