Creating a Mixpanel Plugin with Fastify
Tags: webdev, javascript, node
Published: 2023-08-07 22:46:43

# Tutorial: Creating a Mixpanel Plugin with Fastify

In this tutorial, you will learn how to create a Mixpanel plugin to track errors and request events in a Fastify application using JavaScript. Mixpanel is an analytics platform that allows you to track and analyze user events in applications.

## Step 1: Environment Setup

Make sure you have Node.js installed on your system. If you haven't already, you can download it from [nodejs.org](https://nodejs.org/).

## Step 2: Initializing a Fastify Project

Open a terminal and create a new folder for your project. Navigate to this folder using the terminal and execute the following commands:

```bash
mkdir my-mixpanel-project
cd my-mixpanel-project
npm init -y
npm install fastify mixpanel
```

## Step 3: Creating the Mixpanel Plugin

Create a new file called `mixpanel-plugin.js` in the root folder of your project. Open this file in a code editor and copy the following code:

```javascript
// mixpanel-plugin.js
import mixpanel from 'mixpanel';
import fp from 'fastify-plugin';
import {
  FastifyError,
  FastifyInstance,
  FastifyPluginAsync,
  FastifyRequest,
} from 'fastify';

const mixpanelPlugin: FastifyPluginAsync = fp(
  async (fastify: FastifyInstance, _) => {
    const MIXPANEL_TOKEN: string = process.env.MIXPANEL_TOKEN || '';

    const mixpanelClient = mixpanel.init(MIXPANEL_TOKEN);

    fastify.addHook(
      'onError',
      async (request: FastifyRequest, _, error: FastifyError) => {
        mixpanelClient.track('Error', {
          error: error.message,
          stack: error.stack,
          url: request.url,
        });
      },
    );

    fastify.addHook('onRequest', async (request: FastifyRequest, _) => {
      const eventData = {
        url: request.url,
        params: request.params,
        query: request.query,
        body: request.body,
      };

      mixpanelClient.track(`Request URL ${request.url}`, eventData);
    });
  },
);

export default mixpanelPlugin;
```

## Step 4: Creating the Fastify Application

Create a new file called `app.js` in the root folder of your project. Open this file in a code editor and copy the following code:

```javascript
// app.js
import fastify from 'fastify';
import mixpanelPlugin from './mixpanel-plugin';

const app = fastify();

// Register the Mixpanel plugin
app.register(mixpanelPlugin);

// Define an example route
app.get('/', async (request, reply) => {
  reply.send({ message: 'Hello, world!' });
});

// Start the server
app.listen(3000, (err) => {
  if (err) {
    console.error('Error starting the server:', err);
  } else {
    console.log('Server started on port 3000');
  }
});
```

## Step 5: Running the Application

In the terminal, execute the following command to start the Fastify server:

```bash
node app.js
```

If everything is set up correctly, you will see the message "Server started on port 3000". Now, your application is running, and the Mixpanel plugin will start tracking errors and request events.

## Conclusion

Congratulations! You've created a Mixpanel plugin to track errors and request events in a Fastify application. Now you have a solid foundation for implementing analytics and event tracking in your projects.

Remember to replace `MIXPANEL_TOKEN` with your actual Mixpanel token and adjust the code according to your needs. This tutorial provided an introduction to the concept of plugins in Fastify and how to integrate Mixpanel for event tracking.