This code snippet is a program that creates a tracker image for email open events. It is designed to generate a small transparent image in PNG format that can be embedded in email templates. When the recipient opens the email and the tracker image is loaded, the program triggers an “event:opened” event, allowing you to track when the email is opened. This blog post will provide a detailed explanation of the code with an example.
Code
app.get('/:id/tracker.png', function(request, response, next) {
var emailId = request.param.id;
var buf = new Buffer([
0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x01, 0x00, 0x01, 0x00,
0x80, 0x00, 0x00, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x2c,
0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x02,
0x02, 0x44, 0x01, 0x00, 0x3b
]);
response.set('Content-Type', 'image/png');
response.end(buf, 'binary');
db.findOne({ id: emailId }, function(error, email) {
if(error) return next(error);
app.emit('event:opened', email);
});
});
app.on('event:opened', function(email) {
console.log('Email was opened');
console.log(email.to);
console.log(email.subject);
});Code Explanation
The provided code is written in JavaScript and uses the Express.js framework. Here is a step-by-step explanation of what the code does:
1. The code defines a route in Express.js for the URL pattern ‘/:id/tracker.png’. This route expects a parameter ‘id’, which represents the email ID.
2. Inside the route handler function, the email ID is extracted from the request using the ‘request.param.id’ method and stored in the variable ’emailId’.
3. The program then creates a buffer object using the ‘Buffer’ constructor. The buffer contains the binary data of a small PNG image. This image will be served as the tracker image.
4. The ‘Content-Type’ response header is set to ‘image/png’ to indicate that the response represents an image in PNG format.
5. The tracker image is sent as the response body using the ‘response.end’ method. The ‘binary’ encoding is specified to indicate that the buffer should be interpreted as binary data.
6. After sending the tracker image, the program retrieves the corresponding email from the database using ‘db.findOne’ method. It searches for the email with the matching ID.
7. If there is an error retrieving the email, the program returns the error using the ‘next’ function. This allows the error to be handled by Express.js error middleware.
8. If the email is successfully retrieved, the program emits an ‘event:opened’ event and passes the email object as the argument.
9. Outside the route handler function, the program defines an event listener for the ‘event:opened’ event. This listener logs a message indicating that the email was opened, along with the recipient’s email address and the subject of the email.
Example:
Let’s consider an example to understand how this code works. Suppose we embed a tracker image in an email template with the ID ‘12345’. When a recipient opens the email, their email client makes a request to the ‘/12345/tracker.png’ URL.
The code handling this request extracts the ID ‘12345’ and generates a small transparent PNG image. It then sends this image as the response. Additionally, it retrieves the corresponding email from the database and emits an ‘event:opened’ event.
The event listener logs a message to the console, indicating that the email was opened, along with the recipient’s email address and the subject of the email.
By analyzing the event logs, you can track how many recipients opened the email and gain insights into the effectiveness of your email campaigns.
In conclusion, this code snippet provides a simple and efficient way to track email open events by creating and serving a tracker image. By following the explanation and example provided in this blog post, you can easily implement this functionality in your own email systems. Remember to customize the code according to your specific requirements and integrate it with your existing email templates and database.
Also checkout the following codes.
How to Get Formatted Date and Time using JavaScript
How to Create a Dynamic Greeting Message in React
