Event Handling

Node.js uses an event-driven architecture, making it possible to execute code when a specific event occurs. The discord.js library takes full advantage of this. You can visit the Client documentation to see the full list of events.

At this point, your index.js file has listeners for two events: ClientReady and InteractionCreate.

client.once(Events.ClientReady, (readyClient) => {
	console.log(`Ready! Logged in as ${readyClient.user.tag}`);

client.on(Events.InteractionCreate, async (interaction) => {
	if (!interaction.isChatInputCommand()) return;

	const command = interaction.client.commands.get(interaction.commandName);

	if (!command) {
		console.error(`No command matching ${interaction.commandName} was found.`);
		return;
	}

	try {
		await command.execute(interaction);
	} catch (error) {
		console.error(error);
		if (interaction.replied || interaction.deferred) {
			await interaction.followUp({
				content: 'There was an error while executing this command!',
				flags: MessageFlags.Ephemeral,
			});
		} else {
			await interaction.reply({
				content: 'There was an error while executing this command!',
				flags: MessageFlags.Ephemeral,
			});
		}
	}
});

Currently, the event listeners are in the index.js file. Client#readyemits once when the Client becomes ready for use, and Client#interactionCreate emits whenever an interaction is received. Moving the event listener code into individual files is simple, and we'll be taking a similar approach to the command handler.

Individual event files

Your project directory should look something like this:

Create an events folder in the same directory. You can then move the code from your event listeners in index.js to separate files: events/ready.js and events/interactionCreate.js.

const { Events } = require('discord.js');

module.exports = {
	name: Events.ClientReady,
	once: true,
	execute(client) {
		console.log(`Ready! Logged in as ${client.user.tag}`);
	},
};

The name property states which event this file is for, and the once property holds a boolean value that specifies if the event should run only once. You don't need to specify this in interactionCreate.js as the default behavior will be to run on every event instance. The execute function holds your event logic, which will be called by the event handler whenever the event emits.

Reading event files

Next, let's write the code for dynamically retrieving all the event files in the events folder. We'll be taking a similar approach to our command handler. Place the new code highlighted below in your index.js.

fs.readdirSync().filter() returns an array of all the file names in the given directory and filters for only .js files, i.e. ['ready.js', 'interactionCreate.js'].

const fs = require('node:fs');
const path = require('node:path');
const { Client, Collection, GatewayIntentBits } = require('discord.js');
const { token } = require('./config.json');

const client = new Client({ intents: [GatewayIntentBits.Guilds] });

client.commands = new Collection();
const foldersPath = path.join(__dirname, 'commands');
const commandFolders = fs.readdirSync(foldersPath);

for (const folder of commandFolders) {
	const commandsPath = path.join(foldersPath, folder);
	const commandFiles = fs.readdirSync(commandsPath).filter((file) => file.endsWith('.js'));
	for (const file of commandFiles) {
		const filePath = path.join(commandsPath, file);
		const command = require(filePath);
		if ('data' in command && 'execute' in command) {
			client.commands.set(command.data.name, command);
		} else {
			console.log(`[WARNING] The command at ${filePath} is missing a required "data" or "execute" property.`);
		}
	}
}

const eventsPath = path.join(__dirname, 'events');
const eventFiles = fs.readdirSync(eventsPath).filter((file) => file.endsWith('.js'));

for (const file of eventFiles) {
	const filePath = path.join(eventsPath, file);
	const event = require(filePath);
	if (event.once) {
		client.once(event.name, (...args) => event.execute(...args));
	} else {
		client.on(event.name, (...args) => event.execute(...args));
	}
}

client.login(token);

You'll notice the code looks very similar to the command loading above it - read the files in the events folder and load each one individually.

The Client class in discord.js extends the EventEmitter class. Therefore, the client object exposes the .on() and .once() methods that you can use to register event listeners. These methods take two arguments: the event name and a callback function. These are defined in your separate event files as name and execute.

The callback function passed takes argument(s) returned by its respective event, collects them in an args array using the ... rest parameter syntax, then calls event.execute() while passing in the args array using the ... spread syntax. They are used here because different events in discord.js have different numbers of arguments. The rest parameter collects these variable number of arguments into a single array, and the spread syntax then takes these elements and passes them to the execute function.

After this, listening for other events is as easy as creating a new file in the events folder. The event handler will automatically retrieve and register it whenever you restart your bot.