# 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 Clientopen in new window documentation to see the full list of events.

Here's the base code we'll be using:

const { Client, Intents } = require('discord.js');
const { token } = require('./config.json');

const client = new Client({ intents: [Intents.FLAGS.GUILDS] });

client.once('ready', c => {
	console.log(`Ready! Logged in as ${c.user.tag}`);
});

client.on('interactionCreate', interaction => {
	console.log(`${interaction.user.tag} in #${interaction.channel.name} triggered an interaction.`);
});

client.login(token);

Currently, the event listeners are in the index.js file. Client#event:readyopen in new window emits once when the Client becomes ready for use, and Client#event:interactionCreateopen in new window 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:

discord-bot/
├── node_modules
├── config.json
├── index.js
├── package-lock.json
└── package.json

Create an events folder in the same directory. You can then take your existing events code in index.js and move them to events/ready.js and events/interactionCreate.js files.

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

module.exports = {
	name: 'interactionCreate',
	execute(interaction) {
		console.log(`${interaction.user.tag} in #${interaction.channel.name} triggered an interaction.`);
	},
};

The name property states which event this file is for, and the once property is a boolean that specifies if the event should run only once. The execute function is for 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.

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 client = new Client({ intents: [Intents.FLAGS.GUILDS] });

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));
	}
}

The Clientopen in new window class in discord.js extends the EventEmitteropen in new window class. Therefore, the client object exposes the .on()open in new window and .once()open in new window methods that you can use to register event listeners. These methods take two arguments: the event name and a callback function.

The callback function passed takes argument(s) returned by its respective event, collects them in an args array using the ... rest parameter syntaxopen in new window, then calls event.execute() while passing in the args array using the ... spread syntaxopen in new window. 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.

# Resulting code

If you want to compare your code to the code we've constructed so far, you can review it over on the GitHub repository here open in new window.