handlebars

What is handlebars?

Handlebars is a popular templating engine for JavaScript. It allows you to create templates with dynamic content that can be rendered with different contexts. It is commonly used to generate HTML for web pages, but can also be used for other types of text output.

What are handlebars's main functionalities?

Simple Templating

Handlebars allows you to iterate over an array and generate HTML for each item. In this example, 'people' is an array that is iterated over, and for each item, a paragraph element is created with the content of the item.

{{#each people}}<p>{{this}}</p>{{/each}}

Conditional Statements

You can use conditional statements in your templates to render different HTML based on the context. Here, if 'isAdmin' is true, a button is displayed; otherwise, a paragraph is shown.

{{#if isAdmin}}<button>Admin</button>{{else}}<p>Not an admin</p>{{/if}}

Custom Helpers

Handlebars allows you to define custom helpers that you can use in your templates. In this example, a 'loud' helper is created that converts a string to uppercase.

Handlebars.registerHelper('loud', function (aString) { return aString.toUpperCase(); });

Built-in Helpers

Handlebars provides built-in helpers like 'with' which you can use to change the context within a block. This example shows how to use the 'with' helper to access properties of an object without repeating the object name.

{{#with person}}<p>{{firstName}} {{lastName}}</p>{{/with}}

Partials

Partials are reusable template fragments in Handlebars. You can define a partial and then include it in other templates. This code shows how to include a partial named 'userMessage'.

{{> userMessage}}

Other packages similar to handlebars

mustache

Mustache is a logic-less template syntax that can be used for HTML, config files, source code, etc. It's similar to Handlebars but with fewer features and a focus on simplicity.

pug

Pug, formerly known as Jade, is a high-performance template engine heavily influenced by Haml and implemented with JavaScript for Node.js and browsers. It offers a more terse syntax and compiles to HTML.

ejs

EJS, or Embedded JavaScript templates, is a simple templating language that lets you generate HTML markup with plain JavaScript. It is more straightforward than Handlebars, embedding JavaScript code directly in the template.

README

Handlebars.js

Handlebars.js is an extension to the Mustache templating language created by Chris Wanstrath. Handlebars.js and Mustache are both logicless templating languages that keep the view and the code separated like we all know they should be.

Checkout the official Handlebars docs site at http://www.handlebarsjs.com and the live demo at http://tryhandlebarsjs.com/.

Installing

See our installation documentation.

Usage

In general, the syntax of Handlebars.js templates is a superset of Mustache templates. For basic syntax, check out the Mustache manpage.

Once you have a template, use the Handlebars.compile method to compile the template into a function. The generated function takes a context argument, which will be used to render the template.

var source = "<p>Hello, my name is {{name}}. I am from {{hometown}}. I have " +
             "{{kids.length}} kids:</p>" +
             "<ul>{{#kids}}<li>{{name}} is {{age}}</li>{{/kids}}</ul>";
var template = Handlebars.compile(source);

var data = { "name": "Alan", "hometown": "Somewhere, TX",
             "kids": [{"name": "Jimmy", "age": "12"}, {"name": "Sally", "age": "4"}]};
var result = template(data);

// Would render:
// <p>Hello, my name is Alan. I am from Somewhere, TX. I have 2 kids:</p>
// <ul>
//   <li>Jimmy is 12</li>
//   <li>Sally is 4</li>
// </ul>

Full documentation and more examples are at handlebarsjs.com.

Precompiling Templates

Handlebars allows templates to be precompiled and included as javascript code rather than the handlebars template allowing for faster startup time. Full details are located here.

Differences Between Handlebars.js and Mustache

Handlebars.js adds a couple of additional features to make writing templates easier and also changes a tiny detail of how partials work.

• Nested Paths
• Helpers
• Block Expressions
• Literal Values
• Delimited Comments

Block expressions have the same syntax as mustache sections but should not be confused with one another. Sections are akin to an implicit each or with statement depending on the input data and helpers are explicit pieces of code that are free to implement whatever behavior they like. The mustache spec defines the exact behavior of sections. In the case of name conflicts, helpers are given priority.

Compatibility

There are a few Mustache behaviors that Handlebars does not implement.

• Handlebars deviates from Mustache slightly in that it does not perform recursive lookup by default. The compile time compat flag must be set to enable this functionality. Users should note that there is a performance cost for enabling this flag. The exact cost varies by template, but it's recommended that performance sensitive operations should avoid this mode and instead opt for explicit path references.
• The optional Mustache-style lambdas are not supported. Instead Handlebars provides its own lambda resolution that follows the behaviors of helpers.
• Alternative delimiters are not supported.

Supported Environments

Handlebars has been designed to work in any ECMAScript 3 environment. This includes

• Node.js
• Chrome
• Firefox
• Safari 5+
• Opera 11+
• IE 6+

Older versions and other runtimes are likely to work but have not been formally tested. The compiler requires JSON.stringify to be implemented natively or via a polyfill. If using the precompiler this is not necessary.

Performance

In a rough performance test, precompiled Handlebars.js templates (in the original version of Handlebars.js) rendered in about half the time of Mustache templates. It would be a shame if it were any other way, since they were precompiled, but the difference in architecture does have some big performance advantages. Justin Marney, a.k.a. gotascii, confirmed that with an independent test. The rewritten Handlebars (current version) is faster than the old version, with many performance tests being 5 to 7 times faster than the Mustache equivalent.

Upgrading

See release-notes.md for upgrade notes.

Known Issues

See FAQ.md for known issues and common pitfalls.

Handlebars in the Wild

• Assemble, by @jonschlinkert and @doowb, is a static site generator that uses Handlebars.js as its template engine.
• Cory, by @leo, is another tiny static site generator
• CoSchedule An editorial calendar for WordPress that uses Handlebars.js
• dashbars A modern helper library for Handlebars.js.
• Ember.js makes Handlebars.js the primary way to structure your views, also with automatic data binding support.
• Ghost Just a blogging platform.
• handlebars_assets: A Rails Asset Pipeline gem from Les Hill (@leshill).
• handlebars-helpers is an extensive library with 100+ handlebars helpers.
• handlebars-layouts is a set of helpers which implement extendible and embeddable layout blocks as seen in other popular templating languages.
• hbs: An Express.js view engine adapter for Handlebars.js, from Don Park.
• koa-hbs: koa generator based renderer for Handlebars.js.
• jblotus created http://tryhandlebarsjs.com for anyone who would like to try out Handlebars.js in their browser.
• jQuery plugin: allows you to use Handlebars.js with jQuery.
• Lumbar provides easy module-based template management for handlebars projects.
• Marionette.Handlebars adds support for Handlebars and Mustache templates to Marionette.
• sammy.js by Aaron Quint, a.k.a. quirkey, supports Handlebars.js as one of its template plugins.
• SproutCore uses Handlebars.js as its main templating engine, extending it with automatic data binding support.
• YUI implements a port of handlebars
• Swag by @elving is a growing collection of helpers for handlebars.js. Give your handlebars.js templates some swag son!
• DOMBars is a DOM-based templating engine built on the Handlebars parser and runtime DEPRECATED
• promised-handlebars is a wrapper for Handlebars that allows helpers to return Promises.
• just-handlebars-helpers A fully tested lightweight package with common Handlebars helpers.

External Resources

• Gist about Synchronous and asynchronous loading of external handlebars templates

Have a project using Handlebars? Send us a pull request!

License

Handlebars.js is released under the MIT license.