res.render for templates in Express - Mini Project: Build & Apply

Using res.render to Display Templates in Express

📖 Scenario: You are building a simple web server using Express.js. You want to show a welcome page to users using a template.

🎯 Goal: Create an Express app that uses res.render to display a template called welcome with a message.

📋 What You'll Learn

Create an Express app instance called app

Set the view engine to pug

Create a route for / that uses res.render to show the welcome template

Pass a variable called message with the value 'Hello, visitor!' to the template

💡 Why This Matters

🌍 Real World

Web servers often use templates to create dynamic HTML pages that show different content depending on the user or situation.

💼 Career

Knowing how to use res.render and templates is essential for backend web developers working with Express.js to build user-friendly websites.

1

Set up Express app and import express

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

Express

const express = require('express');
// Your code here

Hint

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

2

Set the view engine to pug

Add code to set the view engine of app to 'pug' using app.set.

Express

const express = require('express');
const app = express();
// Your code here

Hint

Use app.set('view engine', 'pug') to tell Express to use Pug templates.

3

Create a route that renders the welcome template

Write a route handler for GET / on app that calls res.render to render the template named 'welcome' and passes an object with message set to 'Hello, visitor!'.

Express

const express = require('express');
const app = express();
app.set('view engine', 'pug');
// Your code here

Hint

Use app.get('/', (req, res) => { res.render('welcome', { message: 'Hello, visitor!' }) }).

4

Add code to start the server on port 3000

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

Express

const express = require('express');
const app = express();
app.set('view engine', 'pug');

app.get('/', (req, res) => {
    res.render('welcome', { message: 'Hello, visitor!' });
});
// Your code here

Hint

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

Practice

1. What does res.render do in an Express app?

easy

A. It creates and sends an HTML page using a template and data.

B. It sends a JSON response to the client.

C. It redirects the user to another URL.

D. It logs a message to the server console.

Solution

1. Step 1: Understand the purpose of res.render

   res.render is used to create a web page by combining a template with data.

2. Step 2: Identify what res.render sends to the client

   It sends the generated HTML page as the response to the user's browser.

3. Final Answer:

   It creates and sends an HTML page using a template and data. -> Option A

4. Quick Check:

   res.render = sends HTML page [OK]

Hint: Remember: res.render sends HTML, not JSON or redirects [OK]

Common Mistakes:

• Confusing res.render with res.json
• Thinking res.render redirects the user
• Assuming res.render logs info instead of sending response

2. Which of the following is the correct syntax to render a template named 'home' with a variable 'title' set to 'Welcome'?

easy

A. res.render('home', 'title', 'Welcome');

B. res.render('home', { title: 'Welcome' });

C. res.render('home', ['title', 'Welcome']);

D. res.render('home', title = 'Welcome');

Solution

1. Step 1: Check the method signature of res.render

   It takes the template name as first argument and an object with variables as second argument.

2. Step 2: Match the correct object syntax

   The correct way to pass variables is using an object like { title: 'Welcome' }.

3. Final Answer:

   res.render('home', { title: 'Welcome' }); -> Option B

4. Quick Check:

   res.render(template, object) = correct syntax [OK]

Hint: Pass variables as an object, not as separate arguments [OK]

Common Mistakes:

• Passing variables as separate arguments instead of an object
• Using array instead of object for variables
• Assigning variables inside the argument list incorrectly

3. Given this Express code snippet, what will the user see when visiting '/'?

app.get('/', (req, res) => {
  res.render('index', { name: 'Alice' });
});

Assuming the 'index' template contains: <h1>Hello, <%= name %>!</h1>

medium

A. Hello, Alice!

B. Hello, <%= name %>!

C. Error: Template not found

D. Hello, !

Solution

1. Step 1: Understand how res.render passes data to template

   The object { name: 'Alice' } provides the value for name in the template.

2. Step 2: Evaluate the template output

   The template uses <%= name %> to insert the value 'Alice' into the HTML.

3. Final Answer:

   <h1>Hello, Alice!</h1> -> Option A

4. Quick Check:

   Template variable replaced correctly =

   Hello, Alice!

   [OK]

Hint: Variables in template replaced by object keys passed to res.render [OK]

Common Mistakes:

• Expecting raw template tags to appear in output
• Assuming missing template causes silent empty output
• Confusing template syntax with HTML escaping

4. What is wrong with this Express code snippet?

app.get('/about', (req, res) => {
  res.render('about', title: 'About Us');
});

medium

A. res.render cannot be used inside app.get routes.

B. The template name 'about' should be a variable, not a string.

C. The second argument to res.render should be an object, but it's missing curly braces.

D. The route path '/about' is invalid.

Solution

1. Step 1: Check the syntax of res.render arguments

   The second argument must be an object with key-value pairs, but here it's written without curly braces.

2. Step 2: Identify the correct object syntax

   It should be { title: 'About Us' } to pass variables properly.

3. Final Answer:

   The second argument to res.render should be an object, but it's missing curly braces. -> Option C

4. Quick Check:

   res.render second argument = object with braces [OK]

Hint: Always wrap variables in an object with curly braces for res.render [OK]

Common Mistakes:

• Omitting curly braces around variables object
• Passing variables as separate arguments
• Misunderstanding route handler usage

5. You want to render a 'profile' template that shows a user's name and age. The user data is in an object user = { name: 'Bob', age: 30 }. Which code correctly renders the template passing the user data so the template can access name and age directly?

hard

A. res.render('profile', ['name', user.name, 'age', user.age]);

B. res.render('profile', { user });

C. res.render('profile', { name: user, age: user.age });

D. res.render('profile', { name: user.name, age: user.age });

Solution

1. Step 1: Understand how template variables are accessed

   The template expects variables name and age directly, not inside a nested object.

2. Step 2: Pass variables as separate keys in an object

   Passing { name: user.name, age: user.age } makes name and age available directly in the template.

3. Final Answer:

   res.render('profile', { name: user.name, age: user.age }); -> Option D

4. Quick Check:

   Pass variables as keys for direct template access [OK]

Hint: Pass each variable separately for direct template use [OK]

Common Mistakes:

• Passing the whole user object instead of separate keys
• Passing variables as an array instead of object
• Assuming template can access nested object keys without dot notation