When building web applications with Express JS, a common task is to send responses back to the client. res.end() and res.send() are two fundamental methods provided by the response object in Express to accomplish this. This tutorial provides an overview of how to use these methods effectively, with examples ranging from basic to advanced use cases.
Understanding res.end()
The res.end() method is used to end the response process without any data. It is a Node.js response method, inherited by Express. This method tells the server that you have finished handling the response and that the server should consider this message complete. The syntax looks as follows:
res.end([data[, encoding]])It is worth noting that when you call res.end(), no more data can be written to the response.
Basic Example – res.end()
app.get('/', (req, res) => {
res.end('Hello World!');
});Understanding res.send()
The res.send() method is an Express-specific method that sends a response of various types to the client. It is actually more powerful than res.end() because it can handle different types of data automatically, including applying proper content-type headers. The syntax is:
res.send([body])This method not only allows you to set the content of the response but also concludes the response process.
Basic Example – res.send()
app.get('/', (req, res) => {
res.send('Hello World!');
});When to Use res.end() and res.send()
res.end() is used when you want to go no further in detail and simply want to end the response, possibly after sending data. res.send() meanwhile can be used for most cases where you need to send processed data back to the client like HTML, JSON, and even files.
Sending JSON – res.send()
app.get('/user', (req, res) => {
res.send({ name: 'John Doe', age: 30 });
});Sending HTML – res.send()
app.get('/dashboard', (req, res) => {
res.send('<h1>Welcome to your Dashboard</h1>');
});Advanced Use Cases
There are more advanced scenarios where you would want to use these methods in different ways.
Streaming Data
When you want to stream data, you might need to use res.end() to signal that the streaming has finished.
app.get('/stream', (req, res) => {
res.write('Streaming starts...\n');
// Stream your data here
res.end('...Streaming ended.');
});Handling Errors
When handling errors, you might want to use res.send() to send back an error message with a status code.
app.use((err, req, res, next) => {
res.status(500).send('Something broke!');
});Content Negotiation
Express provides ways to do content negotiation out of the box. This example shows how to use req.accepts() to determine the response type.
app.get('/negotiate', (req, res) => {
if (req.accepts('json')) {
res.send({ message: 'JSON content' });
} else if (req.accepts('html')) {
res.send('<p>HTML content</p>');
} else {
res.end();
}
});Conclusion
In conclusion, res.end() and res.send() are handy methods for sending responses to clients in Express JS apps. While res.end() is ideal for quickly finishing the response, res.send() gives more flexibility and is suited for most of the content types you will typically send back to your clients. Understanding when and how to use each method allows for better control over the HTTP response and aids in the development of robust web servers.
