handlebars-lang/handlebars.js

Handlebars.js

Handlebars provides the power necessary to let you build semantic templates effectively with no frustration. Handlebars is largely compatible with Mustache templates. In most cases it is possible to swap out Mustache with Handlebars and continue using your current templates.

Checkout the official Handlebars docs site at handlebarsjs.com and try our live demo.

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.
• Handlebars does not allow space between the opening {{ and a command character such as #, / or >. The command character must immediately follow the braces, so for example {{> partial }} is allowed but {{ > partial }} is not.
• Alternative delimiters are not supported.

Supported Environments

Handlebars has been designed to work in any ECMAScript 2020 environment. This includes

• Node.js
• Chrome
• Firefox
• Safari
• Edge

If you need to support older environments, use Handlebars version 4.

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.

Benchmarks

The project includes a comprehensive benchmark suite (powered by tinybench) that measures compilation, execution, precompilation, and end-to-end performance across templates of varying size and complexity.

# Run benchmarks (auto-labels with current git branch)
pnpm run bench

# Run with a custom label
pnpm run bench -- --label my-optimization

# Filter templates by name (regex, case-insensitive)
pnpm run bench -- --grep "complex|recursive"

# Run only specific sections (regex, case-insensitive)
pnpm run bench -- --section precompil
pnpm run bench -- --section "compilation|precompil"

# Compare results
pnpm run bench:compare

# Or specify files explicitly
pnpm run bench:compare -- bench/results/bench-*-main.md bench/results/bench-*-feat.md

Results are saved as timestamped Markdown files in bench/results/. Each report includes ops/sec, avg latency, p50/p75/p99 percentiles, and sample counts.

Typical workflow for comparing branches:

git checkout main && pnpm run bench
git checkout my-feature && pnpm run bench
pnpm run bench:compare

When run without arguments, bench:compare auto-selects two result files: if a file labelled "main" exists it is always used as the baseline, otherwise the older file is the baseline. The comparison uses p75 latency for the diff to filter outliers, and marks changes with ! (>2%) and !! (>5%).

Upgrading

See release-notes.md for upgrade notes.

If you are using Handlebars in production, please regularly look for issues labeled possibly breaking. If this label is applied to an issue, it means that the requested change is probably not a breaking change, but since Handlebars is widely in use by a lot of people, there's always a chance that it breaks somebody's build.

Known Issues

See FAQ.md for known issues and common pitfalls.

Handlebars in the Wild

• apiDoc apiDoc uses handlebars as parsing engine for api documentation view generation.
• Assemble, by @jonschlinkert and @doowb, is a static site generator that uses Handlebars.js as its template engine.
• CoSchedule An editorial calendar for WordPress that uses Handlebars.js.
• Ember.js makes Handlebars.js the primary way to structure your views, also with automatic data binding support.
• express-handlebars A Handlebars view engine for Express which doesn't suck.
• express-hbs Express Handlebars template engine with inheritance, partials, i18n and async helpers.
• Ghost Just a blogging platform.
• handlebars-action A GitHub action to transform files in your repository with Handlebars templating.
• 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 extensible and embeddable layout blocks as seen in other popular templating languages.
• handlebars-loader A handlebars template loader for webpack.
• handlebars-wax The missing Handlebars API. Effortless registration of data, partials, helpers, and decorators using file-system globs, modules, and plain-old JavaScript objects.
• hbs An Express.js view engine adapter for Handlebars.js, from Don Park.
• html-bundler-webpack-plugin The webpack plugin to compile templates, supports Handlebars.
• incremental-bars adds support for incremental-dom as template target to Handlebars.
• jQuery plugin allows you to use Handlebars.js with jQuery.
• just-handlebars-helpers A fully tested lightweight package with common Handlebars helpers.
• koa-hbs koa generator based renderer for Handlebars.js.
• Marionette.Handlebars adds support for Handlebars and Mustache templates to Marionette.
• openVALIDATION a natural language compiler for validation rules. Generates program code in Java, JavaScript, C#, Python and Rust with handlebars.
• Plop is a micro-generator framework that makes it easy to create files with a level of uniformity.
• promised-handlebars is a wrapper for Handlebars that allows helpers to return Promises.
• sammy.js by Aaron Quint, a.k.a. quirkey, supports Handlebars.js as one of its template plugins.
• Swag by @elving is a growing collection of helpers for handlebars.js. Give your handlebars.js templates some swag son!
• SproutCore uses Handlebars.js as its main templating engine, extending it with automatic data binding support.
• vite-plugin-handlebars A package for Vite 2. Allows for running your HTML files through the Handlebars compiler.
• YUI implements a port of handlebars.

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.