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[![Build Status](https://travis-ci.org/wycats/handlebars.js.png?branch=master)](https://travis-ci.org/wycats/handlebars.js) Handlebars.js ============= Handlebars.js is an extension to the [Mustache templating language](http://mustache.github.com/) 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](http://www.handlebarsjs.com). Installing ---------- Installing Handlebars is easy. Simply download the package [from the official site](http://handlebarsjs.com/) and add it to your web pages (you should usually use the most recent version). Usage ----- In general, the syntax of Handlebars.js templates is a superset of Mustache templates. For basic syntax, check out the [Mustache manpage](http://mustache.github.com/mustache.5.html). 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. ```js 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> ``` Registering Helpers ------------------- You can register helpers that Handlebars will use when evaluating your template. Here's an example, which assumes that your objects have a URL embedded in them, as well as the text for a link: ```js Handlebars.registerHelper('link_to', function() { return "<a href='" + this.url + "'>" + this.body + "</a>"; }); var context = { posts: [{url: "/hello-world", body: "Hello World!"}] }; var source = "<ul>{{#posts}}<li>{{{link_to}}}</li>{{/posts}}</ul>" var template = Handlebars.compile(source); template(context); // Would render: // // <ul> // <li><a href='/hello-world'>Hello World!</a></li> // </ul> ``` Helpers take precedence over fields defined on the context. To access a field that is masked by a helper, a path reference may be used. In the example above a field named `link_to` on the `context` object would be referenced using: ``` {{./link_to}} ``` Escaping -------- By default, the `{{expression}}` syntax will escape its contents. This helps to protect you against accidental XSS problems caused by malicious data passed from the server as JSON. To explicitly *not* escape the contents, use the triple-mustache (`{{{}}}`). You have seen this used in the above example. 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. ### Paths Handlebars.js supports an extended expression syntax that we call paths. Paths are made up of typical expressions and . characters. Expressions allow you to not only display data from the current context, but to display data from contexts that are descendants and ancestors of the current context. To display data from descendant contexts, use the `.` character. So, for example, if your data were structured like: ```js var data = {"person": { "name": "Alan" }, company: {"name": "Rad, Inc." } }; ``` You could display the person's name from the top-level context with the following expression: ``` {{person.name}} ``` You can backtrack using `../`. For example, if you've already traversed into the person object you could still display the company's name with an expression like `{{../company.name}}`, so: ``` {{#person}}{{name}} - {{../company.name}}{{/person}} ``` would render: ``` Alan - Rad, Inc. ``` ### Strings When calling a helper, you can pass paths or Strings as parameters. For instance: ```js Handlebars.registerHelper('link_to', function(title, options) { return "<a href='/posts" + this.url + "'>" + title + "!</a>" }); var context = { posts: [{url: "/hello-world", body: "Hello World!"}] }; var source = '<ul>{{#posts}}<li>{{{link_to "Post"}}}</li>{{/posts}}</ul>' var template = Handlebars.compile(source); template(context); // Would render: // // <ul> // <li><a href='/posts/hello-world'>Post!</a></li> // </ul> ``` When you pass a String as a parameter to a helper, the literal String gets passed to the helper function. ### Block Helpers Handlebars.js also adds the ability to define block helpers. Block helpers are functions that can be called from anywhere in the template. Here's an example: ```js var source = "<ul>{{#people}}<li>{{#link}}{{name}}{{/link}}</li>{{/people}}</ul>"; Handlebars.registerHelper('link', function(options) { return '<a href="/people/' + this.id + '">' + options.fn(this) + '</a>'; }); var template = Handlebars.compile(source); var data = { "people": [ { "name": "Alan", "id": 1 }, { "name": "Yehuda", "id": 2 } ]}; template(data); // Should render: // <ul> // <li><a href="/people/1">Alan</a></li> // <li><a href="/people/2">Yehuda</a></li> // </ul> ``` Whenever the block helper is called it is given one or more parameters, any arguments that are passed in the helper in the call and an `options` object containing the `fn` function which executes the block's child. The block's current context may be accessed through `this`. Block helpers 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](http://mustache.github.io/mustache.5.html) defines the exact behavior of sections. In the case of name conflicts, helpers are given priority. ### Partials You can register additional templates as partials, which will be used by Handlebars when it encounters a partial (`{{> partialName}}`). Partials can either be String templates or compiled template functions. Here's an example: ```js var source = "<ul>{{#people}}<li>{{> link}}</li>{{/people}}</ul>"; Handlebars.registerPartial('link', '<a href="/people/{{id}}">{{name}}</a>') var template = Handlebars.compile(source); var data = { "people": [ { "name": "Alan", "id": 1 }, { "name": "Yehuda", "id": 2 } ]}; template(data); // Should render: // <ul> // <li><a href="/people/1">Alan</a></li> // <li><a href="/people/2">Yehuda</a></li> // </ul> ``` ### Comments You can add comments to your templates with the following syntax: ```js {{! This is a comment }} ``` You can also use real html comments if you want them to end up in the output. ```html <div> {{! This comment will not end up in the output }}  </div> ``` Precompiling Templates ---------------------- Handlebars allows templates to be precompiled and included as javascript code rather than the handlebars template allowing for faster startup time. ### Installation The precompiler script may be installed via npm using the `npm install -g handlebars` command. ### Usage <pre> Precompile handlebar templates. Usage: handlebars template... Options: -a, --amd Create an AMD format function (allows loading with RequireJS) [boolean] -f, --output Output File [string] -k, --known Known helpers [string] -o, --knownOnly Known helpers only [boolean] -m, --min Minimize output [boolean] -s, --simple Output template function only. [boolean] -r, --root Template root. Base value that will be stripped from template names. [string] </pre> If using the precompiler's normal mode, the resulting templates will be stored to the `Handlebars.templates` object using the relative template name sans the extension. These templates may be executed in the same manner as templates. If using the simple mode the precompiler will generate a single javascript method. To execute this method it must be passed to the using the `Handlebars.template` method and the resulting object may be as normal. ### Optimizations - Rather than using the full _handlebars.js_ library, implementations that do not need to compile templates at runtime may include _handlebars.runtime.js_ whose min+gzip size is approximately 1k. - If a helper is known to exist in the target environment they may be defined using the `--known name` argument may be used to optimize accesses to these helpers for size and speed. - When all helpers are known in advance the `--knownOnly` argument may be used to optimize all block helper references. 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. 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](http://github.com/gotascii), confirmed that with an [independent test](http://sorescode.com/2010/09/12/benchmarks.html). The rewritten Handlebars (current version) is faster than the old version, and we will have some benchmarks in the near future. Building -------- To build handlebars, just run `rake release`, and you will get two files in the `dist` directory. Upgrading --------- See [release-notes.md](https://github.com/wycats/handlebars.js/blob/master/release-notes.md) for upgrade notes. Known Issues ------------ * Handlebars.js can be cryptic when there's an error while rendering. * Using a variable, helper, or partial named `class` causes errors in IE browsers. (Instead, use `className`) Handlebars in the Wild ----------------- * [jblotus](http://github.com/jblotus) created [http://tryhandlebarsjs.com](http://tryhandlebarsjs.com) for anyone who would like to try out Handlebars.js in their browser. * Don Park wrote an Express.js view engine adapter for Handlebars.js called [hbs](http://github.com/donpark/hbs). * [sammy.js](http://github.com/quirkey/sammy) by Aaron Quint, a.k.a. quirkey, supports Handlebars.js as one of its template plugins. * [SproutCore](http://www.sproutcore.com) uses Handlebars.js as its main templating engine, extending it with automatic data binding support. * [Ember.js](http://www.emberjs.com) makes Handlebars.js the primary way to structure your views, also with automatic data binding support. * Les Hill (@leshill) wrote a Rails Asset Pipeline gem named [handlebars_assets](http://github.com/leshill/handlebars_assets). * [Gist about Synchronous and asynchronous loading of external handlebars templates](https://gist.github.com/2287070) * [Lumbar](walmartlabs.github.io/lumbar) provides easy module-based template management for handlebars projects. * [YUI](http://yuilibrary.com/yui/docs/handlebars/) implements a port of handlebars Have a project using Handlebars? Send us a [pull request](https://github.com/wycats/handlebars.js/pull/new/master)! Helping Out ----------- To build Handlebars.js you'll need a few things installed. * Node.js * Ruby * therubyracer, for running tests - `gem install therubyracer` * rspec, for running tests - `gem install rspec` There's a Gemfile in the repo, so you can run `bundle` to install rspec and therubyracer if you've got bundler installed. To build Handlebars.js from scratch, you'll want to run `rake compile` in the root of the project. That will build Handlebars and output the results to the dist/ folder. To run tests, run `rake test`. You can also run our set of benchmarks with `rake bench`. Node tests can be run with `npm test` or `rake npm_test`. The default rake target will compile and run both test suites. Some environments, notably Windows, have issues running therubyracer. Under these envrionments the `rake compile` and `npm test` should be sufficient to test most handlebars functionality. If you notice any problems, please report them to the GitHub issue tracker at [http://github.com/wycats/handlebars.js/issues](http://github.com/wycats/handlebars.js/issues). Feel free to contact commondream or wycats through GitHub with any other questions or feature requests. To submit changes fork the project and send a pull request. License ------- Handlebars.js is released under the MIT license.