Sending Response in Express.js

Back to Express.js
Arjit Sharma
01 Min

In Express.js, sending a response is the final step in the request–response cycle. Once a response is sent, the cycle ends and no further actions can be taken on that request.

Common Response Methods

Express provides several methods to send responses of different types: text, JSON, HTML, files, or even redirects.

// Sending plain text
app.get("/", (req, res) => {
  res.send("Hello World");
});

// Sending JSON
app.get("/json", (req, res) => {
  res.json({ message: "Hello, JSON!", status: "success" });
});

// Sending error with status code
app.get("/error", (req, res) => {
  res.status(404).send("Page not found");
});

// Redirecting to another route
app.get("/go-home", (req, res) => {
  res.redirect("/");
});

// Sending a file
const path = require("path");
app.get("/file", (req, res) => {
  res.sendFile(path.join(__dirname, "example.html"));
});

Explanation of Methods

  • res.send() Sends a response of various types: strings, objects, buffers, or HTML. Example: res.send("<h1>Hello HTML</h1>");

  • res.json() Converts JavaScript objects into JSON and automatically sets the Content-Type header to application/json.

  • res.status(code) Sets the HTTP status code for the response. Often chained with res.send() or res.json().

  • res.redirect(url) Redirects the client to another URL. By default, it uses status code 302 (Found).

  • res.sendFile(path) Sends a file as a response. path.join(__dirname, …) is commonly used to safely construct absolute paths.

  • res.set(header, value) Allows setting custom headers. Example: res.set(“X-App-Version”, “1.0”);

Common Status Codes

Status CodeMeaning
200Success
201Resource created
400Bad request
401Unauthorized
404Not found
500Server error

Best Practices

  • Always send a response for every request to avoid hanging connections.
  • Use appropriate status codes to make APIs predictable and RESTful.
  • Prefer res.json() for APIs since it ensures proper headers and structured data.
  • When serving files, use res.sendFile() with absolute paths for security.
  • Add custom headers when needed (e.g., versioning, caching)
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