Request and Response objects in Deno - Mini Project: Build & Apply

Handling Request and Response Objects in Deno

📖 Scenario: You are building a simple web server using Deno. Your server will receive HTTP requests and send back responses. Understanding how to work with Request and Response objects is essential to handle client-server communication.

🎯 Goal: Build a basic Deno server that reads the incoming Request object, checks the request method, and sends back a Response object with a message.

📋 What You'll Learn

Create a variable to hold the server listener

Add a variable to store the expected HTTP method

Use the Request object to check the method of incoming requests

Send a Response object with a text message based on the request method

💡 Why This Matters

🌍 Real World

Web servers need to handle HTTP requests and send responses correctly. Understanding Request and Response objects is key to building APIs and web applications.

💼 Career

Backend developers and full-stack engineers use these concepts daily to create web services and handle client communication.

1

Create the server listener

Create a variable called server and assign it the result of Deno.listen({ port: 8080 }) to start listening on port 8080.

Deno

# Your code here
// Create the server listener on port 8080

Hint

Use Deno.listen with an object specifying port: 8080.

2

Set the expected HTTP method

Add a variable called expectedMethod and set it to the string "GET" to specify the HTTP method your server will handle.

Deno

const server = Deno.listen({ port: 8080 })
// Define the expected HTTP method
# Your code here

Hint

Use const expectedMethod = "GET" to store the method.

3

Check the request method

Write an async function called handleRequest that takes a Request object named request. Inside, use an if statement to check if request.method equals expectedMethod. Return a Response with the text "Hello from GET" if true, otherwise return a Response with "Method not allowed" and status 405.

Deno

const server = Deno.listen({ port: 8080 })
const expectedMethod = "GET"

// Write async function handleRequest(request)
# Your code here

Hint

Use request.method to check the HTTP method and return appropriate Response objects.

4

Complete the server to handle requests

Add a for await loop over server to accept connections. Inside, create an HTTP connection from each connection using Deno.serveHttp(conn). Then, use another for await loop over httpConn to get each request event. For each event, call handleRequest(event.request) and respond with event.respondWith() using the returned Response.

Deno

const server = Deno.listen({ port: 8080 })
const expectedMethod = "GET"

async function handleRequest(request) {
    if (request.method === expectedMethod) {
        return new Response("Hello from GET", { status: 200 })
    } else {
        return new Response("Method not allowed", { status: 405 })
    }
}

// Add for await loop to accept connections and respond to requests
# Your code here

Hint

Use nested for await loops to accept connections and handle HTTP requests asynchronously.

Practice

1. What does the Request object represent in a Deno web server?

easy

A. The data sent by the server to the user

B. The server's file system access

C. The server configuration settings

D. The data sent by the user to the server

Solution

1. Step 1: Understand the role of Request object

   The Request object contains information about what the user sends to the server, such as headers, method, and body.

2. Step 2: Differentiate from Response object

   The Response object is what the server sends back, so it is not the Request.

3. Final Answer:

   The data sent by the user to the server -> Option D

4. Quick Check:

   Request = user data [OK]

Hint: Request = user input; Response = server output [OK]

Common Mistakes:

• Confusing Request with Response
• Thinking Request holds server settings
• Assuming Request is server output

2. Which of the following is the correct way to create a Response object with a JSON body in Deno?

easy

A. Response.json(data)

B. new Response(data, { type: 'json' })

C. new Response(data, { headers: { 'Content-Type': 'application/json' } })

D. new Response(data, { contentType: 'application/json' })

Solution

1. Step 1: Check how to send JSON in Response

   In Deno, you can create a Response with JSON by stringifying the data and setting the 'Content-Type' header to 'application/json'.

2. Step 2: Validate options

   new Response(data, { headers: { 'Content-Type': 'application/json' } }) correctly sets the header and passes data (assuming data is stringified). Response.json(data) is invalid because Response.json() is not a standard method in Deno's Response API. Options B and D use incorrect properties.

3. Final Answer:

   new Response(data, { headers: { 'Content-Type': 'application/json' } }) -> Option C

4. Quick Check:

   Response with JSON header [OK]

Hint: Use new Response(JSON.stringify(data), { headers: { 'Content-Type': 'application/json' } }) [OK]

Common Mistakes:

• Passing raw object without stringify
• Using incorrect init properties like 'type' or 'contentType'
• Assuming Response.json() exists

3. Given the following Deno server code snippet, what will be the response body when a user sends a GET request?

const handler = (req) => {
  if (req.method === 'GET') {
    return new Response('Hello World');
  }
  return new Response('Method Not Allowed', { status: 405 });
};

medium

A. "Method Not Allowed"

B. "Hello World"

C. Empty response

D. Error thrown

Solution

1. Step 1: Check request method condition

   The code checks if the request method is 'GET'. If yes, it returns 'Hello World'.

2. Step 2: Determine response for GET request

   Since the user sends a GET request, the first condition matches and returns 'Hello World'.

3. Final Answer:

   "Hello World" -> Option B

4. Quick Check:

   GET request returns 'Hello World' [OK]

Hint: Check req.method to decide response content [OK]

Common Mistakes:

• Ignoring method check and picking wrong response
• Assuming default response is empty
• Thinking error is thrown on GET

4. Identify the error in this Deno request handler code:

const handler = (req) => {
  if (req.method = 'POST') {
    return new Response('Posted');
  }
  return new Response('Not Posted');
};

medium

A. Using assignment (=) instead of comparison (===) in if condition

B. Missing await keyword before Response

C. Response body must be JSON, not string

D. req.method is undefined

Solution

1. Step 1: Check the if condition syntax

   The code uses single equals (=) which assigns 'POST' to req.method instead of comparing it.

2. Step 2: Understand correct comparison operator

   To compare, use '===' or '==' instead of '=' to avoid bugs.

3. Final Answer:

   Using assignment (=) instead of comparison (===) in if condition -> Option A

4. Quick Check:

   Use '===' for comparison, not '=' [OK]

Hint: Use '===' for comparisons, '=' is assignment [OK]

Common Mistakes:

• Confusing assignment and comparison operators
• Thinking Response needs await here
• Assuming req.method is missing

5. How can you read JSON data sent in the body of a POST request using the Deno Request object?

hard

A. Use await req.json() to parse the JSON body

B. Use req.body.json() without await

C. Use JSON.parse(req.body) directly

D. Use req.getJson() method

Solution

1. Step 1: Understand how to parse JSON body in Deno

   The Request object has an async method json() that returns the parsed JSON from the body.

2. Step 2: Confirm correct usage

   You must await req.json() because it returns a Promise resolving to the parsed object.

3. Final Answer:

   Use await req.json() to parse the JSON body -> Option A

4. Quick Check:

   await req.json() parses JSON body correctly [OK]

Hint: Always await req.json() to get JSON body [OK]

Common Mistakes:

• Calling json() without await
• Trying to parse req.body directly
• Using non-existent getJson() method