Request and response management is one of the fundamental concepts in any web application. In Express, the interaction between the client and server is based on receiving HTTP requests and sending responses. In this chapter, we will learn how to handle these requests and responses in Express, from accessing request parameters, bodies, and headers to sending responses with different status codes and formats.

Understanding the Request

Every time a client makes a request to a server, Express creates a req (request) object that contains all the information related to that request, such as parameters, body, cookies, and headers.

Accessing Route Parameters

When a route is defined in Express, we can access the dynamic parameters that are part of the URL using req.params.

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Accessing Query Parameters

Query parameters are those passed in the URL after the question mark ?. Express makes them available through req.query.

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Accessing the Request Body

To access the body of a request (usually in POST or PUT requests), we need to use the middleware express.json() or express.urlencoded() if the data is in JSON format or form format.

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Accessing Request Headers

HTTP headers provide additional information about the request. We can access headers using req.headers.

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Sending Responses

In Express, the res (response) object is used to send responses back to the client. We can send responses in various formats like text, JSON, and redirections.

Sending Text Responses

We can send a simple text response using res.send().

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Sending JSON Responses

To send responses in JSON format, we use res.json().

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Setting HTTP Status Codes

HTTP status codes indicate the result of a request. We can set a status code using res.status().

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Redirecting Requests

We can redirect clients to a new URL using res.redirect().

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Sending Files

Express also allows sending files as a response using res.sendFile().

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Middleware for Handling Requests and Responses

Middleware in Express is a function that can intercept requests and responses in the application's lifecycle. Middlewares are commonly used to authenticate users, validate data, or log events.

Request Logging Middleware

We can create middleware to log all requests received by the application.

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Error Handling Middleware

To manage errors in a centralized manner, we can use error-handling middleware.

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Best Practices for Handling Requests and Responses

1. Input Validation: Always validate request data before processing it to prevent errors and security vulnerabilities.
2. Header Security: Use tools like helmet to secure HTTP headers and prevent common attacks such as clickjacking or cross-site scripting (XSS).
3. Efficient Response Sending: Try to minimize the size of responses by using compression or sending only necessary data to improve performance.
4. Error Handling: Implement a global error handling system to capture any problems and prevent responses with sensitive information from being sent to clients.

Conclusion

In this chapter, we have learned how Express handles HTTP requests and responses, from accessing request parameters and bodies to sending responses in different formats and setting status codes. This knowledge is essential for building robust and efficient web applications.