Template partials and layouts in Express - Mini Project: Build & Apply

Template Partials and Layouts in Express

📖 Scenario: You are building a simple website using Express and EJS templates. You want to reuse common parts of your pages like the header and footer, and have a main layout that wraps your content.

🎯 Goal: Create an Express app that uses EJS templates with a layout and partials for header and footer. Render a home page that uses these partials inside the layout.

📋 What You'll Learn

Create a main layout template called layout.ejs with a placeholder for page content

Create partial templates called header.ejs and footer.ejs

Include the header.ejs and footer.ejs partials inside the layout

Render a home page index.ejs that uses the layout and displays a welcome message

💡 Why This Matters

🌍 Real World

Web developers often use template partials and layouts to avoid repeating code and keep their HTML organized and maintainable.

💼 Career

Understanding how to use layouts and partials in Express with EJS is a common skill required for building scalable web applications.

1

Set up Express app and EJS view engine

Create an Express app in app.js. Set the view engine to ejs using app.set('view engine', 'ejs').

Express

// Your code here to create Express app and set view engine to ejs

Hint

Use import express from 'express' and then const app = express(). Set the view engine with app.set('view engine', 'ejs').

2

Create layout and partial templates

Create a file views/layout.ejs with HTML structure. Inside it, include the partials header.ejs and footer.ejs using <%- include('header') %> and <%- include('footer') %>. Add a placeholder <%- body %> where page content will go.

Express

import express from 'express';
const app = express();
app.set('view engine', 'ejs');

// Create layout.ejs with header and footer partials and body placeholder
// Your code here

Hint

Use EJS syntax <%- include('filename') %> to include partials. Use <%- body %> to insert page content.

3

Create header and footer partials

Create views/header.ejs with a <header> containing a site title inside an <h1>. Create views/footer.ejs with a <footer> containing a copyright notice.

Express

import express from 'express';
const app = express();
app.set('view engine', 'ejs');

// Create header.ejs with My Website
// Create footer.ejs with © 2024 My Website
// Your code here

Hint

Write simple HTML inside header.ejs and footer.ejs files with the exact text.

4

Render home page using layout and partials

Create views/index.ejs with a <p> that says Welcome to the home page!. In app.js, add a route for / that renders index.ejs using the layout by passing the content as body.

Express

import express from 'express';
const app = express();
app.set('view engine', 'ejs');

// Create index.ejs with Welcome to the home page!
// Add route for '/' that renders index.ejs with layout
// Your code here

Hint

Use app.get('/', (req, res) => { res.render('layout', { body: '...' }) }) to render the home page content inside the layout.

Practice

1. What is the main purpose of using template partials in Express apps?

easy

A. To define the main layout structure for all pages

B. To reuse small template parts like headers or footers across pages

C. To write JavaScript logic inside templates

D. To connect the app to a database

Solution

1. Step 1: Understand what partials are

   Partials are small pieces of templates like headers or footers that you can reuse.

2. Step 2: Differentiate partials from layouts

   Layouts provide the main page structure, while partials are smaller reusable parts inside layouts or pages.

3. Final Answer:

   To reuse small template parts like headers or footers across pages -> Option B

4. Quick Check:

   Partials = reusable small template parts [OK]

Hint: Partials = small reusable pieces like header/footer [OK]

Common Mistakes:

• Confusing partials with layouts
• Thinking partials define full page structure
• Assuming partials handle backend logic

2. Which syntax correctly includes a partial named header in an EJS template?

easy

A. <%- include('header') %>

B. <%= partial('header') %>

C. <% include header %>

D. <@include header>

Solution

1. Step 1: Recall EJS partial include syntax

   EJS uses <%- include('partialName') %> to include partials with unescaped output.

2. Step 2: Check each option

   <%- include('header') %> matches the correct syntax with parentheses and quotes around 'header'.

3. Final Answer:

   <%- include('header') %> -> Option A

4. Quick Check:

   EJS partial include = <%- include('name') %> [OK]

Hint: EJS partials use <%- include('name') %> syntax [OK]

Common Mistakes:

• Omitting quotes or parentheses in include
• Using <%= instead of <%- for unescaped output
• Confusing syntax with other template engines

3. Given this Express setup using EJS with a layout:

app.set('view engine', 'ejs');

// In route handler:
res.render('index', { title: 'Home' });

And the layout layout.ejs contains:

<html>
<head><title><%= title %></title></head>
<body>
<%- body %>
</body>
</html>

If index.ejs has <h1>Welcome</h1>, what will the rendered HTML look like?

medium

A. Welcome

B. Home<h1>Welcome</h1>

C. HomeWelcome

D. Error: body is undefined

Solution

1. Step 1: Understand layout and body insertion

   The layout uses <%- body %> to insert the rendered content of index.ejs unescaped.

2. Step 2: Check variable substitution

   The title variable is passed as 'Home', so <%= title %> becomes 'Home'. The body inserts <h1>Welcome</h1> as HTML.

3. Final Answer:

   <html><head><title>Home</title></head><body><h1>Welcome</h1></body></html> -> Option C

4. Quick Check:

   Layout inserts title and body correctly [OK]

Hint: Layout inserts body unescaped with <%- body %> [OK]

Common Mistakes:

• Using escaped output <%= body %> causing HTML to show as text
• Not passing title variable to template
• Assuming body variable is automatic without layout support

4. You try to use a layout in Express with EJS but get an error: ReferenceError: body is not defined. What is the likely cause?

medium

A. You forgot to use a layout engine or middleware that injects the body content

B. You used <%= body %> instead of <%- body %>

C. You named your layout file incorrectly

D. You did not install EJS package

Solution

1. Step 1: Understand how layouts work in Express with EJS

   EJS alone does not support layouts natively; you need middleware like express-ejs-layouts to inject body content.

2. Step 2: Identify cause of ReferenceError

   If body is undefined, it means the layout engine or middleware that sets body is missing or not configured.

3. Final Answer:

   You forgot to use a layout engine or middleware that injects the body content -> Option A

4. Quick Check:

   Missing layout middleware = body undefined error [OK]

Hint: Layouts need middleware to define body variable [OK]

Common Mistakes:

• Assuming EJS supports layouts without extra setup
• Confusing escaped vs unescaped output errors
• Ignoring middleware installation or configuration

5. You want to create a consistent site with a header, footer, and main content area using Express and EJS. Which approach best uses partials and layouts together?

hard

A. Use only partials for header, footer, and content without any layout file

B. Include header and footer partials directly in every page template without a layout

C. Write all HTML in each page template without partials or layouts

D. Create a layout.ejs with header and footer partials included, and insert page content in a <%- body %> area

Solution

1. Step 1: Understand roles of layouts and partials

   Layouts provide the main page structure; partials are reusable pieces like header and footer.

2. Step 2: Combine layout and partials for best practice

   Put header and footer partials inside the layout, then insert page-specific content in the body area.

3. Final Answer:

   Create a layout.ejs with header and footer partials included, and insert page content in a <%- body %> area -> Option D

4. Quick Check:

   Layout + partials = clean, consistent site structure [OK]

Hint: Use layout for structure, partials for reusable parts [OK]

Common Mistakes:

• Duplicating header/footer in every page instead of partials
• Skipping layout causing inconsistent page structure
• Mixing content and layout roles improperly