GET route handling in Express - Mini Project: Build & Apply

Express GET Route Handling

📖 Scenario: You are building a simple web server that responds to user requests. You want to create a route that listens for GET requests on a specific path and sends back a friendly message.

🎯 Goal: Create an Express server with a GET route at /hello that responds with the text Hello, Express!.

📋 What You'll Learn

Create an Express app instance called app

Set up a GET route on /hello

Send the response Hello, Express! when the route is accessed

Listen on port 3000

💡 Why This Matters

🌍 Real World

Web servers often need to respond to user requests on different paths. GET routes are the most common way to serve pages or data.

💼 Career

Understanding how to handle GET routes in Express is essential for backend web development jobs using Node.js.

1

Set up Express app

Write code to import Express and create an app instance called app.

Express

# Import express and create app instance
# Your code here

Hint

Use require('express') to import Express and then call it to create app.

2

Create GET route

Add a GET route on /hello using app.get that takes req and res as parameters.

Express

const express = require('express');
const app = express();

// Add GET route for /hello
# Your code here

Hint

Use app.get('/hello', (req, res) => { ... }) to create the route.

3

Send response text

Inside the GET route callback, use res.send to send the text Hello, Express!.

Express

const express = require('express');
const app = express();

app.get('/hello', (req, res) => {
    // Send response text
    # Your code here
});

Hint

Use res.send('Hello, Express!') inside the route callback.

4

Start server on port 3000

Add code to make the app listen on port 3000 using app.listen.

Express

const express = require('express');
const app = express();

app.get('/hello', (req, res) => {
    res.send('Hello, Express!');
});

// Start server on port 3000
# Your code here

Hint

Use app.listen(3000) to start the server on port 3000.

Practice

1. What does the app.get() method do in an Express app?

easy

A. Starts the Express server and listens on a port

B. Defines a route to handle GET requests at a specific URL

C. Sends a POST request to a server

D. Deletes a route from the Express app

Solution

1. Step 1: Understand the purpose of app.get()

   The app.get() method is used to define a route that listens for GET requests on a given URL path.

2. Step 2: Compare with other methods

   Other methods like app.post() handle POST requests, and app.listen() starts the server, so they do not define GET routes.

3. Final Answer:

   Defines a route to handle GET requests at a specific URL -> Option B

4. Quick Check:

   app.get() defines GET routes [OK]

Hint: app.get() always sets up a GET route handler [OK]

Common Mistakes:

• Confusing app.get() with app.listen()
• Thinking app.get() sends requests instead of handling them
• Mixing GET with POST methods

2. Which of the following is the correct syntax to create a GET route for the path /hello that sends "Hello World" as a response?

easy

A. app.get('/hello', (req, res) => { res.send('Hello World'); });

B. app.get('/hello', (res, req) => { res.send('Hello World'); });

C. app.get('/hello', (req, res) => { res.write('Hello World'); });

D. app.get('/hello', (req, res) => { res.sendHello('Hello World'); });

Solution

1. Step 1: Check parameter order in callback

   The callback function parameters must be req first, then res. app.get('/hello', (res, req) => { res.send('Hello World'); }); reverses them, which is incorrect.

2. Step 2: Verify response method usage

   The correct method to send a response string is res.send(). app.get('/hello', (req, res) => { res.write('Hello World'); }); uses res.write() which is not standard in Express, and app.get('/hello', (req, res) => { res.sendHello('Hello World'); }); uses a non-existent method res.sendHello().

3. Final Answer:

   app.get('/hello', (req, res) => { res.send('Hello World'); }); -> Option A

4. Quick Check:

   Correct syntax uses req, res and res.send() [OK]

Hint: Use (req, res) and res.send() to respond in GET routes [OK]

Common Mistakes:

• Swapping req and res parameters
• Using res.write() instead of res.send()
• Calling non-existent response methods

3. What will be the output when a GET request is made to /user/42 with this route handler?

app.get('/user/:id', (req, res) => {
  res.send(`User ID is ${req.params.id}`);
});

medium

A. User ID is undefined

B. User ID is :id

C. Error: req.params is not defined

D. User ID is 42

Solution

1. Step 1: Understand route parameters

   The route /user/:id captures the part after /user/ as req.params.id.

2. Step 2: Substitute parameter in response

   When visiting /user/42, req.params.id is "42", so the response is "User ID is 42".

3. Final Answer:

   User ID is 42 -> Option D

4. Quick Check:

   Route params fill req.params.id correctly [OK]

Hint: Use req.params to get URL parts in routes [OK]

Common Mistakes:

• Using req.params without defining route parameter
• Expecting literal ':id' in output
• Forgetting to use backticks for template strings

4. Identify the error in this GET route handler:

app.get('/data', (req, res) => {
  res.send('Data received')
  res.send('Another response');
});

medium

A. Missing semicolon after first res.send()

B. Route path should be '/data/' with trailing slash

C. Cannot call res.send() twice in the same request handler

D. req parameter is unused and causes error

Solution

1. Step 1: Check response sending rules

   Express allows sending only one response per request. Calling res.send() twice causes an error.

2. Step 2: Analyze other options

   Missing semicolons do not cause runtime errors here, trailing slash is optional, and unused parameters do not cause errors.

3. Final Answer:

   Cannot call res.send() twice in the same request handler -> Option C

4. Quick Check:

   Only one res.send() per request allowed [OK]

Hint: Send response only once per route handler [OK]

Common Mistakes:

• Calling res.send() multiple times
• Thinking missing semicolons cause errors
• Confusing trailing slash necessity

5. You want to create a GET route /product/:category/:id that responds with a message like "Category: electronics, ID: 123". Which code correctly implements this?

hard

A. app.get('/product/:category/:id', (req, res) => { res.send(`Category: ${req.params.category}, ID: ${req.params.id}`); });

B. app.get('/product/:category/:id', (req, res) => { res.send('Category: req.params.category, ID: req.params.id'); });

C. app.get('/product/:category/:id', (res, req) => { res.send(`Category: ${req.params.category}, ID: ${req.params.id}`); });

D. app.get('/product/:category/:id', (req, res) => { res.send(`Category: ${req.query.category}, ID: ${req.query.id}`); });

Solution

1. Step 1: Use correct parameter order and template literals

   The callback must have (req, res) and use backticks with ${} to insert variables. app.get('/product/:category/:id', (req, res) => { res.send(`Category: ${req.params.category}, ID: ${req.params.id}`); }); does this correctly.

2. Step 2: Use req.params for URL parameters

   Route parameters are accessed via req.params, not req.query. app.get('/product/:category/:id', (req, res) => { res.send(`Category: ${req.query.category}, ID: ${req.query.id}`); }); incorrectly uses req.query. app.get('/product/:category/:id', (req, res) => { res.send('Category: req.params.category, ID: req.params.id'); }); uses quotes, so variables won't be evaluated. app.get('/product/:category/:id', (res, req) => { res.send(`Category: ${req.params.category}, ID: ${req.params.id}`); }); swaps parameters.

3. Final Answer:

   app.get('/product/:category/:id', (req, res) => { res.send(`Category: ${req.params.category}, ID: ${req.params.id}`); }); -> Option A

4. Quick Check:

   Use req.params and template literals correctly [OK]

Hint: Use req.params and backticks for dynamic route responses [OK]

Common Mistakes:

• Swapping req and res parameters
• Using string quotes instead of template literals
• Using req.query instead of req.params for route params