Building a Discord bot with Node.js and Repl.it

In this tutorial, we’ll use repl.it and Node.js to build a Discord Chatbot. The bot will be able to join a Discord server and respond to messages sent by people.

If you don’t like JavaScript, there’s also a Python version of this tutorial.

You’ll find it easier to follow along if you have some JavaScript knowledge and you should have used Discord or a similar app such as Skype or Telegram before. We won’t be covering the very basics of Node.js, but we will explain each line of code in detail, so if you have any experience with programming, you should be able to follow along.

Setting up

We’ll be doing all of our coding through the Repl.it web IDE and hosting our bot with Repl.it as well, so you won’t need to install any additional software on your machine.

For set up, we’ll be walking through the following steps. Skip any that don’t apply to you (e.g. if you already have a Discord account, you can skip that section).

  • Creating an account on Repl.it.

  • Creating an account on Discord.

  • Creating an application and a bot user in your Discord account

  • Creating a server on Discord

  • Adding our bot to our Discord server

Let’s get through these admin steps first and then we can get to the fun part of coding our bot.

Creating an account on Repl.it

Repl.it is an online IDE and compute provider. Traditionally, you would write code locally on your machine, and then have to “deploy” the code to a server, so that other people on the internet could interact with it. Repl.it removes one of these steps by combining the two – you can write your code directly through the Repl.it interface and it will automatically be deployed to the public internet.

Visit Repl.it in your web browser and hit the “Sign up” button.

Repl.it sign up button Image 1: Signing up for Repl

After signing up, press “Start coding now” and choose “Node.js” from the list of available languages.

Play around with the interface a bit to see how easy it is to write and run code. We’ll be coming back to this interface soon after we’ve done some of the Discord set up.

Creating a bot in Discord and getting a token

If you’re reading this tutorial, you probably have at least heard of Discord and likely have an existing account. If not, Discord is a VoIP and Chat application that is designed to replace Skype for gamers. You can sign up for a free account over at the Discord register page, and download one of their desktop or mobile applications from the Discord homepage.

Once you have an account, you’ll want to create a Discord application. Visit the Discord developer’s page and press the “Create new application” button, as in the image below. (I’ve already created two applications. If you haven’t, you’ll only see the button that I’ve marked in red and not the two above it.)

Discord create application page Image 2: Creating a new Discord application

The first thing to do on the next page is to note your Client ID, which you’ll need to add the bot to the server. You can come back later and get if from this page, or copy it somewhere where you can easily find it later.

Fill out a name and description for your bot (feel free to be more creative than me) and press “save changes”.

Naming our Discord bot Image 3: Naming our Discord Application

Now you’ve created a Discord application. The next step is to add a bot to this application, so head over to the “Bot” tab using the menu on the left and press the “Add Bot” button, as indicated below. Click “yes, do it” when Discord asks if you’re sure about bringing a new bot to life.

Adding a bot to our Discord application Image 4: Adding a bot to our Discord Application

The last thing we’ll need from our bot is a Token. Anyone who has the bot’s Token can prove that they own the bot, so you’ll need to be careful not to share this with anyone. You can get the token by pressing “Click to reveal token”, or copy it to your clipboard without seeing it by pressing “Copy”.

Getting a Token for your bot Image 5: Generating a token for our Discord bot

Take note of your Token or copy it to your clipboard, as we’ll need to add it to our code soon.

Creating a Discord server

If you don’t have a Discord server to add your bot to, you can create one by opening the desktop Discord application that you downloaded earlier. Press the “+” icon as shown below to create a server. Creating a discord server Image 6: Creating a Discord server

Press “Create a server” in the screen that follows, and then give your server a name. Once the server is up and running, you can chat to yourself, or invite some friends to chat with you. Soon we’ll invite our bot to chat with us as well.

Adding your Discord bot to your Discord server

Our Discord bot is still just a shell at this stage as we haven’t written any code to allow him to do anything, but let’s go ahead and add him to our Discord server anyway. To add a bot to your server, you’ll need the Client ID from the “General Information” page that we looked at before (this is the one outlined in green in Image 3, not the Bot Secret from Image 5).

Create a URL that looks as follows, but using your Client ID instead of mine at the end:

Visit the URL that you created in your web browser and you’ll see a page similar to the following where you can choose which server to add your bot to.

Authorizing your bot to join your server Image 7: Authorizing our bot to join our server

After pressing “authorize”, you should get an in-app Discord notification telling you that your bot has joined your server.

Now we can get to the fun part of building a brain for our bot!

Creating a Repl and installing our Discord dependencies

The first thing we need to do is create a Node.js Repl to write the code for our Discord bot. Over at repl.it, create a new Repl, as you did right at the start of this tutorial, choosing “Node.js” as your language again.

We don’t need to reinvent the wheel as there is already a great Node wrapper for the Discord bot API called discord.js. Normally we would install this third-party library through npm, but because we’re using Repl.it, we can skip the installation. Our Repl will automatically pull in all dependencies.

In the default index.js file that is included with your new Repl, add the following line of code.

const Discord = require('discord.js');

Press the “Run” button and you should see Repl installing the Discord library in the output pane on the right, as in the image below.

installing Discord.js Image 8: Installing Discord.js in our Repl.

Our bot is nearly ready to go – but we still need to plug in our secret token. This will authorize our code to control our bot.

Setting up authorization for our bot

By default, Repl code is public. This is great as it encourages collaboration and learning, but we need to be careful not to share our secret bot token (which gives anyone who has access to it full control of our bot).

To get around the problem of needing to give our code access to the token while allowing others to access our code but not our token, we’ll be using environment variables. On a normal machine, we’d set these directly on our operating system, but using Repl we don’t have access to this. Repl allows us to set secrets in environment variables through a special .env file. Create a new file called exactly .env by using the new file button in the left pane and add a variable to define your Bot’s secret token (note that this is the second token that we got while setting up the Bot – different from the Client ID that we used to add our bot to our server). It should looks something like:

DISCORD_BOT_SECRET=NDcUN5T32zcTjMYOM0Y1MTUy.Dk7JBw.ihrTSAO1GKHZSonqvuhtwta16WU

You’ll need to: * Replace the token below (after the = sign) with the token that Discord gave you when creating your own bot. * Be careful about spacing. Unlike in Python, if you put a space on either side of the = in your .env file, these spaces will be part of the variable name or the value, so make sure you don’t have any spaces around the = or at the end of the line. * Run the code again. Sometimes you’ll need to refresh the whole page to make sure that your environment variables are successfully loaded.

DISCORD_BOT_SECRET=NDcUN5T32zcTjMYOM0Y1MTUy.Dk7JBw.ihrTSAO1GKHZSonqvuhtwta16WU

In the image below you we’ve highlighted the “Add file” button, the new file (.env) and how to deine the secret token for our bot’s use.

Creating our .env file Image 9: Creating our .env file

Let’s make a slightly Discord bot that repeats everything we say but in reverse. We can do this in only a few lines of code. In your index.js file, add the following:

const Discord = require('discord.js');
const client = new Discord.Client();
const token = process.env.DISCORD_BOT_SECRET;

client.on('ready', () => {
  console.log("I'm in");
  console.log(client.user.username);
});

client.on('message', msg => {
    if (msg.author.id != client.user.id) {
        msg.channel.send(msg.content.split('').reverse().join(''));
    }
});

client.login(token);

Let’s tear this apart line by line to see what it does.

  • Line 1 is what we had earlier. This line both tells Repl to install the third party library and brings it into this file so that we can use it.

  • In line 2, we create a Discord Client. We’ll use this client to send commands to the Discord server to control our bot and send it commands.

  • In line 3 we retrieve our secret token from the environment variables (which Repl set from our .env file).

  • In line 5, we define an event for our client, which defines how our bot should react to the “ready” event. The Discord bot is going to run asynchronously, which might be a bit confusing if you’re used to running standard synchronous code. We won’t go into asynchronous coding in depth here, but if you’re interested in what this is and why it’s used, there’s a good guide over at RisingStack. In short, instead of running the code in our file from top to bottom, we’ll be running pieces of code in response to specific events.

  • In lines 6-8 we define how our bot should respond to the “ready” event, which is fired when our bot successfully joins a server. We instruct our bot to output some information server side (i.e. this will be displayed in our Repl’s output, but not sent as a message through to Discord). We’ll print a simple I'm in message to see that the bot is there and print our bot’s username (if you’re running multiple bots, this will make it easier to work out who’s doing what).

  • Lines 10-14 are similar, but instead of responding to an “ready” event, we tell our bot how to handle new messages. Line 11 says we only want to respond to messages that aren’t from us (otherwise our bot will keep responding to himself – you can remove this line to see why that’s a problem), and line 12 says we’ll send a new message to the same channel where we received a message (msg.channel) and the content we’ll send will be the same message that we received, but backwards. To reverse a string, we split it into its individual characters, reverse the resulting array, and then join it all back into a string again.

The last line fires up our bot and uses the token we loaded earlier to log into Discord.

Press the big green “Run” button again and you should see your bot reporting a successful channel join in the Repl output.

Repl output showing channel join Image 10: Seeing our bot join our server

Over in your Discord app, send a message and see your Bot respond!

Messages from our bot Image 11: Our bot can talk!

Keeping our bot alive

Your bot can now respond to messages, but only for as long as your Repl is running. If you close your browser tab or shut down your computer, your bot will stop and no longer respond to messages on Discord.

Repl will keep your code running after you close the browser tab only if you are running a web server. Our bot doesn’t require an explicit web server to run, but we can create a server and run it in the background just to keep our Repl alive.

Create a new file in your project called keep_alive.js and add the following code:

var http = require('http');

http.createServer(function (req, res) {
  res.write("I'm alive");
  res.end();
}).listen(8080);

We won’t go over this in detail as it’s not central to our bot, but here we start a web server that will return “I’m alive” if anyone visits it.

In our index.js file, we need to add a require statement for this server at the top. Add the following line near the top of index.js.

const keep_alive = require('./keep_alive.js')

After doing this and hitting the green “Run” button again, you should see some changes to your Repl. For one, you’ll see a new pane in the top right which shows the web output from your server. We can see that visiting our Repl now returns a basic web page showing the “I’m alive” string that we told our web server to return by default.

Running a Node server in the background Image 12 Output from our Node server

Now your bot will stay alive even after closing your browser or shutting down your development machine. Repl will still clean up your server and kill your bot after about one hour of inactivity, so if you don’t use your bot for a while, you’ll have to log into Repl and start the bot up again. Alternatively, you can set up a third-party (free!) service like Uptime Robot. Uptime Robot pings your site every 5 minutes to make sure it’s still working – usually to notify you of unexpected downtime, but in this case the constant pings have the side effect of keeping our Repl alive as it will never go more than an hour without receiving any activity. Note that you need to select the HTTP option instead of the Ping option when setting up Uptime Robot as repl.it requires regular HTTP requests to keep your chatbot alive.

Forking and extending our basic bot

This is not a very useful bot as is, but the possibilities are only limited by your creativity now! You can have your bot receive input from a user, process the input, and respond in any way you choose. In fact, with the basic input and output that we’ve demonstrated, we have most of the components of any modern computer, all of which are based on the Von Neumann architecture (we could easily add the missing memory by having our bot write to a file, or with a bit more effort link in a SQLite database for persistent storage).

If you followed along this tutorial, you’ll have your own basic Repl bot to play around with and extend. If you were simply reading, you can easily fork my bot at https://repl.it/@GarethDwyer1/discord-bot-node and extend it how you want (you’ll need to add your own token and recreate the .env file still). Happy hacking!

If you’re stuck for ideas, why not link up your Discord bot to the Twitch API to get notified when your favourite streamers are online, or build a text adventure. Also join Repl’s Discord server by using this invite link https://discord.gg/QWFfGhy - you can test your bot, share it with other bot builders to get feedback, and see what Discord bots people are building on Repl.

If you enjoyed this tutorial, you might also enjoy my tutorial on building a chatbot for Telegram or my book Flask by Example where I show how to build Python applications using the Flask framework. If you have any questions or comments about this tutorial, feel free to reach out on Twitter.