pug template engine interview questions

Mastering Pug Template Engine Top Interview Questions and Answers

Pug (formerly known as Jade) has become one of the most popular templating engines for Node.js due to its clean and easy-to-read syntax. As a developer having a strong command over Pug can help you stand out during technical interviews. In this comprehensive guide, I will provide some of the most frequently asked Pug interview questions that test your knowledge of Pug’s core concepts advanced features, integration with Node.js frameworks, and real-world applications.

Let’s get started!

What is Pug and How Does it Work?

Pug is a high-performance template engine that compiles Pug templates into HTML. It uses indentation rather than closing tags to represent nested elements. This results in cleaner and more readable code compared to plain HTML.

Under the hood, Pug maintains a tree representation of the HTML structure. When a template is compiled, this abstract syntax tree is transformed into corresponding HTML markup which can be served to the client. The compilation step allows Pug to optimize and validate the output before generating HTML.

Some key advantages of using Pug over plain HTML include:

• More concise and cleaner syntax
• Support for variables, mixins and reusable blocks
• Client-side compilation for templating on browser
• Integration with Node.js frameworks like Express

Core Concepts in Pug

Q1. What is the difference between Pug and Jade?

Originally called Jade, the project was later renamed to Pug due to trademark issues. Pug and Jade are essentially the same templating engines – the underlying technology remains unchanged. The transition from Jade to Pug was purely due to naming conflicts.

Q2. How does Pug simplify writing HTML?

Pug minimizes the boilerplate in HTML through:

• Indentation-based nesting for representing structure
• No closing tags required
• Shorthand syntax for ids, classes, attributes
• Mixins for reusing code blocks
• Extends for inheritance
• Includes for break up code into smaller files

This templating syntax results in more compact and cleaner templates compared to plain HTML.

Q3. What are some key features of Pug?

Some notable features of Pug include:

• Whitespace sensitive syntax
• Dynamic code generation using JavaScript
• Template inheritance and mixins
• Native support for Express engine
• Client-side browser support
• Live compilation for development
• Robust API for customization
• Active open-source community

Q4. How does Pug simplify writing nested elements?

Pug relies on indentation rather than closing tags to represent nested element structures. Child elements are indented from their parent elements. This convention eliminates the need for closing tags and gives Pug templates a clean, nested appearance.

For example:

div  h1 Title  p Content 

The <p> tag is nested inside <div> based on indentation rather than close tags.

Q5. Can you explain the difference between buffered and unbuffered code in Pug?

In Pug, buffered code outputs directly into the rendered HTML. Unbuffered code runs but does not output to HTML.

For example:

- var username = "John" // unbuffered, does not outputp= "Hello " + username // buffered, outputs "Hello John"

Buffered code starts with = whereas unbuffered code starts with -. Buffered code escapes characters by default while unbuffered code does not escape.

Pug Syntax and Features

Q6. How do you write comments in Pug?

Pug supports both single line and multi-line comments:

// This is a single line comment /* This is a multi-line     block comment.*/

We can also combine // and /* */ syntax:

//  This is a multi-line  comment using //  

Comments are useful for leaving notes and documentation within Pug templates.

Q7. How do you output plain text in Pug?

We can output plain text using the | character. For multi-line text blocks, use a . after |:

p  | This text will   | output   | as-isp.  This is a   multi-line  plain text block

The . after | informs Pug that this is a text block that retains all whitespace.

Q8. How are variables interpolated in Pug?

Pug variables are interpolated using the #{ } syntax. For example:

- var name = "John"p Hello #{name}

This outputs <p>Hello John</p>. JavaScript expressions can also be embedded within #{ }.

Q9. How do you conditionally output content in Pug?

We can use if, else if, and else to conditionally render content. For example:

- var user = { admin: true }if user.admin  p You are an adminelse  p You are not an admin 

Conditional statements must always start on a new line beginning with -. The conditional blocks are nested based on indentation.

Q10. How do you iterate over arrays and objects in Pug?

Pug provides an each construct to iterate over arrays and objects:

- var users = ["John", "Jane"]each user in users  li= user

This will output a <li> for each user in the array. We can also iterate over keys and values of an object:

- var user = {name: "John", age: 20}each val, key in user  p #{key} : #{val}

The iteration syntax makes it easy to build lists dynamically.

Q11. How are mixins useful in Pug?

Mixins allow you to define reusable blocks of Pug code that can be included in multiple templates. For example:

mixin list  ul    li Item 1    li Item 2 +list+list

This list mixin can now be reused throughout the templates. Mixins are useful for header, footer, widgets and repeated UI patterns.

Integrating Pug with Node.js

Q12. How do you configure Pug as the template engine in an Express app?

To use Pug templates in Express:

1. Install Pug: npm install pug

2. Require Express and Pug modules

3. Set the view engine to use Pug:

app.set('view engine', 'pug')

1. Set the views directory:

app.set('views', path.join(__dirname, 'views')) 

1. Render Pug templates using res.render():

res.render('index') 

This will render index.pug in the views folder.

Q13. How does Pug integrate with Node.js frameworks like Express?

Pug provides out-of-the-box integration with Express and other Node.js frameworks via npm packages. Some key advantages are:

• The express-pug middleware enables Pug rendering
• Pug is set as the default view engine in Express apps
• The res.render() method can be used to render Pug templates
• Pug files can be passed localized variables from routes
• Live reloading available during development
• Caching and localization support

The tight integration makes Pug a natural choice for use with Node.js web frameworks.

Q14. Can you share an example using Pug with Express?

Here is a simple Pug app with Express:

index.js:

const express = require('express')const app = express()app.set('view engine', 'pug')app.get('/', (req, res) => {  res.render('index', {title: 'Home Page'}) })app.listen(3000)

views/index.pug:

h1= titlep Welcome to my app  

This renders index.pug, passing it a title variable. The variable is interpolated using #{title}.

Q15. How do you serve static assets like CSS and images in Pug?

The express.static middleware can be used to serve static assets. For example:

app.use(express.static('public'))

This will serve assets from the public folder. In Pug templates, reference them using root relative path:

link(rel='stylesheet', href='/styles.css') img(src='/logo.png')

The assets will be served from the public folder while retaining the root relative URLs in Pug files.

Advanced Pug Questions

Q16. Can you explain template inheritance in Pug?

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