Title: Using Handlebars with Express.js

Handlebars is a popular templating engine that allows you to build dynamic HTML content by separating the logic from the presentation. It is known for its simplicity and powerful features like helpers, partials, and templates. This chapter will guide you through setting up Handlebars with Express.js, creating dynamic content, using helpers and partials, and following best practices for efficient web application development.

A. Introduction to Handlebars Template Engine

Handlebars is a logic-less templating engine, meaning it doesn't include complex logic within templates. Instead, it focuses on the presentation layer, making it easy to create clean, maintainable, and reusable HTML templates.

Key Features of Handlebars:
- Logic-less templates ensure a clean separation between HTML and JavaScript.
- Supports helpers and partials for code reuse and modularity.
- Can be used both on the server side with Node.js and on the client side in the browser.
Example of Handlebars Syntax:
```
<h1>{{title}}</h1>
<p>Welcome to {{websiteName}}!</p>
```
Explanation:
Handlebars uses {{}} (double curly braces) to output variables and {{#}} for block helpers (like loops and conditionals).

B. Setting Up Handlebars with Express.js

To use Handlebars in your Express.js project, you'll need to install it and configure Express to use Handlebars as the view engine.

Steps to Set Up Handlebars:

Install Handlebars:
```
npm install express-handlebars
```

Configure Express.js to Use Handlebars:

const express = require("express");
const exphbs = require("express-handlebars");
const app = express();

// Set up Handlebars as the view engine
app.engine("handlebars", exphbs());
app.set("view engine", "handlebars");

app.get("/", (req, res) => {
  res.render("home", { title: "Home Page", websiteName: "MyWebsite" });
});### Chapter 16: Using Handlebars with Express.js

C. Introduction to Handlebars Template Engine

Key Features of Handlebars:
- Logic-less templates ensure a clean separation between HTML and JavaScript.
- Supports helpers and partials for code reuse and modularity.
- Can be used both on the server side with Node.js and on the client side in the browser.
Example of Handlebars Syntax:
```
<h1>{{title}}</h1>
<p>Welcome to {{websiteName}}!</p>
```
Explanation:
Handlebars uses {{}} (double curly braces) to output variables and {{#}} for block helpers (like loops and conditionals).

D. Setting Up Handlebars with Express.js

To use Handlebars in your Express.js project, you'll need to install it and configure Express to use Handlebars as the view engine.

Steps to Set Up Handlebars:

Install Handlebars:
```
npm install express-handlebars
```

Configure Express.js to Use Handlebars:

const express = require('express');
const exphbs = require('express-handlebars');
const app = express();

// Set up Handlebars as the view engine
app.engine('handlebars', exphbs());
app.set('view engine', 'handlebars');

app.get('/', (req, res) => {
  res.render('home', { title: 'Home Page', websiteName: 'MyWebsite' });
});

const PORT = 3000;
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});

Create Your Handlebars Templates:
- Create a views directory in your project root.
- Add a file home.handlebars inside the views directory:
```
<h1>{{title}}</h1>
<p>Welcome to {{websiteName}}!</p>
```

Explanation:
The res.render() method is used to render the home.handlebars template and pass variables to it. Handlebars then generates the HTML based on the provided data.

E. Creating Dynamic Content with Handlebars

Handlebars allows you to create dynamic content by embedding variables, looping through data, and using conditionals within your templates.

Passing Data to Handlebars Templates:

app.get('/about', (req, res) => {
  res.render('about', {
    title: 'About Us',
    description: 'This is an about page created using Handlebars.'
  });
});

Using Variables, Loops, and Conditionals in Handlebars:
```
<h1>{{title}}</h1>
<p>{{description}}</p>

<ul>
  {{#each items}}
    <li>{{this}}</li>
  {{/each}}
</ul>

{{#if isAdmin}}
  <p>Welcome, Admin!</p>
{{else}}
  <p>Welcome, User!</p>
{{/if}}
```
Explanation:
In this example, the about.handlebars template uses the title and description variables passed from the route handler. The {{#each}} helper is used to loop through an array, and {{#if}} is used for conditionals.

F. Using Handlebars Helpers and Partials

Handlebars supports helpers and partials, which are essential for creating modular and reusable templates.

Creating and Using Helpers:

Helpers are functions that can be called from within templates to perform specific tasks.

const exphbs = require('express-handlebars');

const hbs = exphbs.create({
  helpers: {
    shout: function (text) {
      return text.toUpperCase();
    },
    formatDate: function (date) {
      return new Date(date).toLocaleDateString();
    }
  }
});

app.engine('handlebars', hbs.engine);

Use the helper in a template:

<h1>{{shout title}}</h1>
<p>Today's date is {{formatDate date}}</p>

Creating and Using Partials:
- Partials are reusable templates that can be included in other templates.
- Create a partial file header.handlebars in the views/partials directory:
```
<header>
  <h1>{{title}}</h1>
  <nav>
    <ul>
      <li><a href="/">Home</a></li>
      <li><a href="/about">About</a></li>
      <li><a href="/contact">Contact</a></li>
    </ul>
  </nav>
</header>
```
- Include the partial in another template:
```
{{> header }}

<main>
  <p>Welcome to the home page.</p>
</main>
```
Explanation:
Helpers are used to manipulate data or perform logic within your templates. Partials allow you to break down your templates into smaller, reusable components.

G. Best Practices with Handlebars

Organize Your Templates:
Structure your Handlebars files in a way that is easy to navigate. Use folders for different sections of your site and keep your layouts, partials, and pages organized.
Use Layouts and Partials Effectively:
Make use of layouts and partials to avoid repeating code. This not only reduces redundancy but also makes your codebase easier to maintain.
Minimize Logic in Templates:
Keep your business logic separate from your templates. The Handlebars templates should focus on rendering HTML, while the application logic should reside in your route handlers or controllers.
Use Helpers Wisely:
Helpers should be used for simple operations. Avoid writing complex logic within helpers, as it can make your templates harder to read and maintain.
Handle Errors Gracefully:
Always include error handling when rendering templates to prevent your application from crashing if something goes wrong.

Conclusion

Handlebars is a powerful and flexible templating engine that integrates seamlessly with Express.js. By understanding how to set up and use Handlebars, you can create dynamic, reusable, and maintainable web applications. The use of helpers, partials, and best practices will help you build scalable applications that are easy to maintain and extend.

 const PORT = 3000;
 app.listen(PORT, () => {
   console.log(`Server is running on port ${PORT}`);
 });
 ```

3. Create Your Handlebars Templates: - Create a views directory in your project root. - Add a file home.handlebars inside the views directory: handlebars <h1>{{title}}</h1> <p>Welcome to {{websiteName}}!</p>

Explanation:
The res.render() method is used to render the home.handlebars template and pass variables to it. Handlebars then generates the HTML based on the provided data.

H. Creating Dynamic Content with Handlebars

Handlebars allows you to create dynamic content by embedding variables, looping through data, and using conditionals within your templates.

Passing Data to Handlebars Templates:

app.get("/about", (req, res) => {
  res.render("about", {
    title: "About Us",
    description: "This is an about page created using Handlebars.",
  });
});

Using Variables, Loops, and Conditionals in Handlebars:
```
<h1>{{title}}</h1>
<p>{{description}}</p>

<ul>
  {{#each items}}
    <li>{{this}}</li>
  {{/each}}
</ul>

{{#if isAdmin}}
  <p>Welcome, Admin!</p>
{{else}}
  <p>Welcome, User!</p>
{{/if}}
```
Explanation:
In this example, the about.handlebars template uses the title and description variables passed from the route handler. The {{#each}} helper is used to loop through an array, and {{#if}} is used for conditionals.

I. Using Handlebars Helpers and Partials

Handlebars supports helpers and partials, which are essential for creating modular and reusable templates.

Creating and Using Helpers:

Helpers are functions that can be called from within templates to perform specific tasks.

const exphbs = require("express-handlebars");

const hbs = exphbs.create({
  helpers: {
    shout: function (text) {
      return text.toUpperCase();
    },
    formatDate: function (date) {
      return new Date(date).toLocaleDateString();
    },
  },
});

app.engine("handlebars", hbs.engine);

Use the helper in a template:

<h1>{{shout title}}</h1>
<p>Today's date is {{formatDate date}}</p>

Creating and Using Partials:
- Partials are reusable templates that can be included in other templates.
- Create a partial file header.handlebars in the views/partials directory:
```
<header>
  <h1>{{title}}</h1>
  <nav>
    <ul>
      <li><a href="/">Home</a></li>
      <li><a href="/about">About</a></li>
      <li><a href="/contact">Contact</a></li>
    </ul>
  </nav>
</header>
```
- Include the partial in another template:
```
{{> header }}

<main>
  <p>Welcome to the home page.</p>
</main>
```
Explanation:
Helpers are used to manipulate data or perform logic within your templates. Partials allow you to break down your templates into smaller, reusable components.

J. Best Practices with Handlebars

Organize Your Templates:
Structure your Handlebars files in a way that is easy to navigate. Use folders for different sections of your site and keep your layouts, partials, and pages organized.
Use Layouts and Partials Effectively:
Make use of layouts and partials to avoid repeating code. This not only reduces redundancy but also makes your codebase easier to maintain.
Minimize Logic in Templates:
Keep your business logic separate from your templates. The Handlebars templates should focus on rendering HTML, while the application logic should reside in your route handlers or controllers.
Use Helpers Wisely:
Helpers should be used for simple operations. Avoid writing complex logic within helpers, as it can make your templates harder to read and maintain.
Handle Errors Gracefully:
Always include error handling when rendering templates to prevent your application from crashing if something goes wrong.