How to Use Request and Response in Deno: Simple Guide

In Deno, you handle HTTP Request and Response objects inside an async function that receives a Request and returns a Response. Use the fetch event or serve from the standard library to listen for requests and send back responses.

Syntax

In Deno, a typical HTTP handler is an async function that takes a Request object and returns a Response object. The Request contains details about the incoming HTTP request, and the Response defines what you send back to the client.

• Request: Holds method, headers, URL, and body.
• Response: Contains status code, headers, and body to send.

typescript

async function handler(req: Request): Promise<Response> {
  // process req
  return new Response("Hello from Deno", { status: 200 });
}

Example

This example shows a simple HTTP server using Deno's serve function. It listens on port 8000, reads the request method and URL, and sends back a plain text response.

typescript

import { serve } from "https://deno.land/std@0.203.0/http/server.ts";

serve(async (req: Request) => {
  const url = new URL(req.url);
  if (req.method === "GET" && url.pathname === "/") {
    return new Response("Welcome to Deno server!", {
      status: 200,
      headers: { "content-type": "text/plain" },
    });
  } else {
    return new Response("Not Found", { status: 404 });
  }
}, { port: 8000 });

Output

Server running on http://localhost:8000
When you visit http://localhost:8000/ you see: Welcome to Deno server!

Common Pitfalls

Some common mistakes when using Request and Response in Deno:

• Not returning a Response object from the handler function causes the server to hang or error.
• Forgetting to set the correct Content-Type header can make the client misinterpret the response.
• Trying to read the request body multiple times without cloning it will fail because the body stream can be read only once.

typescript

/* Wrong: Missing Response return */
serve(async (req) => {
  console.log(req.method);
  // No return here causes error
});

/* Right: Always return a Response */
serve(async (req) => {
  return new Response("OK", { status: 200 });
});

Quick Reference

Here is a quick summary of key points when working with Request and Response in Deno:

• Request: Use req.method, req.url, req.headers, and await req.text() or await req.json() to read body.
• Response: Create with new Response(body, { status, headers }).
• Use serve from std/http/server.ts to start a server easily.
• Always return a Response from your handler.

Key Takeaways

Handle HTTP requests in Deno by writing an async function that takes a Request and returns a Response.

Use the standard library's serve function to listen for requests and send responses easily.

Always return a Response object with proper status and headers to avoid server errors.

Read request body only once and set correct Content-Type headers in responses.

Use URL and method from Request to route and handle different endpoints.