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
https://handlebarsjs.com/ and the live demo at http://tryhandlebarsjs.com/.
See our installation documentation.
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.
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.
Handlebars.js adds a couple of additional features to make writing
templates easier and also changes a tiny detail of how partials work.
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.
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.
Handlebars has been designed to work in any ECMAScript 3 environment. This includes
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.
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.
See release-notes.md for upgrade notes.
See FAQ.md for known issues and common pitfalls.
Have a project using Handlebars? Send us a pull request!
Handlebars.js is released under the MIT license.