mustache

What is mustache?

The mustache npm package is a template engine that uses tags to replace variables in a template string with actual values. It is often used for generating HTML, configuration files, or any other text-based formats in a clean and maintainable way. Mustache is logic-less because it does not have any explicit control flow statements, like if or loop constructs; instead, it relies on the presence or absence of data to control the flow of the document.

What are mustache's main functionalities?

Variable substitution

Substitutes the {{name}} tag with the actual name provided in the data object.

"Hello, {{name}}!"

Section rendering

Renders the section only if the 'logged_in' data property is truthy.

"{{#logged_in}}Welcome, {{user}}!{{/logged_in}}"

Inverted sections

Renders the section only if the 'logged_in' data property is falsy.

"{{^logged_in}}Please log in.{{/logged_in}}"

Comment

Includes a comment in the template that will not be included in the output.

"Today{{! ignore me }} is a sunny day."

Partial views

Includes a partial template named 'user_info' into the current template.

"{{> user_info}}"

Other packages similar to mustache

handlebars

Handlebars is an extension of Mustache that adds support for more complex expressions like helpers and block expressions. It is more feature-rich but also more complex.

ejs

EJS, or Embedded JavaScript templates, allows for more traditional JavaScript code within templates. It is more flexible but can be less maintainable due to the potential for complex logic in templates.

pug

Formerly known as Jade, Pug is a high-performance template engine heavily influenced by Haml and implemented with JavaScript for Node.js and browsers. It has a different syntax that some may find cleaner and more readable.

README

mustache.js - Logic-less {{mustache}} templates with JavaScript

What could be more logical awesome than no logic at all?

mustache.js is an implementation of the mustache template system in JavaScript.

Mustache is a logic-less template syntax. It can be used for HTML, config files, source code - anything. It works by expanding tags in a template using values provided in a hash or object.

We call it "logic-less" because there are no if statements, else clauses, or for loops. Instead there are only tags. Some tags are replaced with a value, some nothing, and others a series of values.

For a language-agnostic overview of mustache's template syntax, see the mustache(5) manpage.

Where to use mustache.js?

You can use mustache.js to render mustache templates anywhere you can use JavaScript. This includes web browsers, server-side environments such as node, and CouchDB views.

mustache.js ships with support for both the CommonJS module API and the Asynchronous Module Definition API, or AMD.

Who uses mustache.js?

An updated list of mustache.js users is kept on the Github wiki. Add yourself or your company if you use mustache.js!

Usage

Below is quick example how to use mustache.js:

var view = {
  title: "Joe",
  calc: function () {
    return 2 + 4;
  }
};

var output = Mustache.render("{{title}} spends {{calc}}", view);

In this example, the Mustache.render function takes two parameters: 1) the mustache template and 2) a view object that contains the data and code needed to render the template.

Templates

A mustache template is a string that contains any number of mustache tags. Tags are indicated by the double mustaches that surround them. {{person}} is a tag, as is {{#person}}. In both examples we refer to person as the tag's key.

There are several types of tags available in mustache.js.

Variables

The most basic tag type is a simple variable. A {{name}} tag renders the value of the name key in the current context. If there is no such key, nothing is rendered.

All variables are HTML-escaped by default. If you want to render unescaped HTML, use the triple mustache: {{{name}}}. You can also use & to unescape a variable.

View:

{
  "name": "Chris",
  "company": "<b>GitHub</b>"
}

Template:

* {{name}}
* {{age}}
* {{company}}
* {{{company}}}
* {{&company}}

Output:

* Chris
*
* <b>GitHub</b>
* <b>GitHub</b>
* <b>GitHub</b>

JavaScript's dot notation may be used to access keys that are properties of objects in a view.

View:

{
  "name": {
    "first": "Michael",
    "last": "Jackson"
  },
  "age": "RIP"
}

Template:

* {{name.first}} {{name.last}}
* {{age}}

Output:

* Michael Jackson
* RIP

Sections

Sections render blocks of text one or more times, depending on the value of the key in the current context.

A section begins with a pound and ends with a slash. That is, {{#person}} begins a person section, while {{/person}} ends it. The text between the two tags is referred to as that section's "block".

The behavior of the section is determined by the value of the key.

False Values or Empty Lists

If the person key does not exist, or exists and has a value of null, undefined, or false, or is an empty list, the block will not be rendered.

View:

{
  "person": false
}

Template:

Shown.
{{#person}}
Never shown!
{{/person}}

Output:

Shown.

Non-Empty Lists

If the person key exists and is not null, undefined, or false, and is not an empty list the block will be rendered one or more times.

When the value is a list, the block is rendered once for each item in the list. The context of the block is set to the current item in the list for each iteration. In this way we can loop over collections.

View:

{
  "stooges": [
    { "name": "Moe" },
    { "name": "Larry" },
    { "name": "Curly" }
  ]
}

Template:

{{#stooges}}
<b>{{name}}</b>
{{/stooges}}

Output:

<b>Moe</b>
<b>Larry</b>
<b>Curly</b>

When looping over an array of strings, a . can be used to refer to the current item in the list.

View:

{
  "musketeers": ["Athos", "Aramis", "Porthos", "D'Artagnan"]
}

Template:

{{#musketeers}}
* {{.}}
{{/musketeers}}

Output:

* Athos
* Aramis
* Porthos
* D'Artagnan

If the value of a section variable is a function, it will be called in the context of the current item in the list on each iteration.

View:

{
  "beatles": [
    { "firstName": "John", "lastName": "Lennon" },
    { "firstName": "Paul", "lastName": "McCartney" },
    { "firstName": "George", "lastName": "Harrison" },
    { "firstName": "Ringo", "lastName": "Starr" }
  ],
  "name": function () {
    return this.firstName + " " + this.lastName;
  }
}

Template:

{{#beatles}}
* {{name}}
{{/beatles}}

Output:

* John Lennon
* Paul McCartney
* George Harrison
* Ringo Starr

Functions

If the value of a section key is a function, it is called with the section's literal block of text, un-rendered, as its first argument. The second argument is a special rendering function that uses the current view as its view argument. It is called in the context of the current view object.

View:

{
  "name": "Tater",
  "bold": function () {
    return function (text, render) {
      return "<b>" + render(text) + "</b>";
    }
  }
}

Template:

{{#bold}}Hi {{name}}.{{/bold}}

Output:

<b>Hi Tater.</b>

Inverted Sections

An inverted section opens with {{^section}} instead of {{#section}}. The block of an inverted section is rendered only if the value of that section's tag is null, undefined, false, or an empty list.

View:

{
  "repos": []
}

Template:

{{#repos}}<b>{{name}}</b>{{/repos}}
{{^repos}}No repos :({{/repos}}

Output:

No repos :(

Comments

Comments begin with a bang and are ignored. The following template:

<h1>Today{{! ignore me }}.</h1>

Will render as follows:

<h1>Today.</h1>

Comments may contain newlines.

Partials

Partials begin with a greater than sign, like {{> box}}.

Partials are rendered at runtime (as opposed to compile time), so recursive partials are possible. Just avoid infinite loops.

They also inherit the calling context. Whereas in ERB you may have this:

<%= partial :next_more, :start => start, :size => size %>

Mustache requires only this:

{{> next_more}}

Why? Because the next_more.mustache file will inherit the size and start variables from the calling context. In this way you may want to think of partials as includes, or template expansion, even though it's not literally true.

For example, this template and partial:

base.mustache:
<h2>Names</h2>
{{#names}}
  {{> user}}
{{/names}}

user.mustache:
<strong>{{name}}</strong>

Can be thought of as a single, expanded template:

<h2>Names</h2>
{{#names}}
  <strong>{{name}}</strong>
{{/names}}

In mustache.js an object of partials may be passed as the third argument to Mustache.render. The object should be keyed by the name of the partial, and its value should be the partial text.

Set Delimiter

Set Delimiter tags start with an equals sign and change the tag delimiters from {{ and }} to custom strings.

Consider the following contrived example:

* {{ default_tags }}
{{=<% %>=}}
* <% erb_style_tags %>
<%={{ }}=%>
* {{ default_tags_again }}

Here we have a list with three items. The first item uses the default tag style, the second uses ERB style as defined by the Set Delimiter tag, and the third returns to the default style after yet another Set Delimiter declaration.

According to ctemplates, this "is useful for languages like TeX, where double-braces may occur in the text and are awkward to use for markup."

Custom delimiters may not contain whitespace or the equals sign.

Plugins for JavaScript Libraries

mustache.js may be built specifically for several different client libraries, including the following:

• jQuery
• MooTools
• Dojo
• YUI
• qooxdoo

These may be built using Rake and one of the following commands:

$ rake jquery
$ rake mootools
$ rake dojo
$ rake yui
$ rake qooxdoo

Testing

The mustache.js test suite uses the vows testing framework. In order to run the tests you'll need to install node. Once that's done you can install vows using npm.

$ npm install -g vows

Then run the tests.

$ vows --spec

The test suite consists of both unit and integration tests. If a template isn't rendering correctly for you, you can make a test for it by doing the following:

1. Create a template file named mytest.mustache in the test/_files directory. Replace mytest with the name of your test.
2. Create a corresponding view file named mytest.js in the same directory. This file should contain a JavaScript object literal enclosed in parentheses. See any of the other view files for an example.
3. Create a file with the expected output in mytest.txt in the same directory.

Then, you can run the test with:

$ TEST=mytest vows test/render_test.js

Thanks

mustache.js wouldn't kick ass if it weren't for these fine souls:

• Chris Wanstrath / defunkt
• Alexander Lang / langalex
• Sebastian Cohnen / tisba
• J Chris Anderson / jchris
• Tom Robinson / tlrobinson
• Aaron Quint / quirkey
• Douglas Crockford
• Nikita Vasilyev / NV
• Elise Wood / glytch
• Damien Mathieu / dmathieu
• Jakub Kuźma / qoobaa
• Will Leinweber / will
• dpree
• Jason Smith / jhs
• Aaron Gibralter / agibralter
• Ross Boucher / boucher
• Matt Sanford / mzsanford
• Ben Cherry / bcherry
• Michael Jackson / mjijackson

Changelog

[0.7.1] / 6 Dec 2012

• Handle empty templates gracefully. Fixes [#265], [#267], and [#270].
  • Cache partials by template, not by name. Fixes [#257].
  • Added Mustache.compileTokens to compile the output of Mustache.parse. Fixes [#258].