0.4.3 • Public • Published

haml-js - Server side templating language for JavaScript

Ever wanted to use the excellent HAML syntax on a javascript project? Me too, so I made one!. This has most of the same functionality as the traditional haml.

About the language

Here is the first example(with a little extra added) from the haml site converted to haml-js:


!!! XML
!!! strict
%html{ xmlns: "http://www.w3.org/1999/xhtml" }
    %title Sample haml template
        #date= print_date()
        #address= current_user.address
        #email= current_user.email
        #bio= current_user.bio


<?xml version='1.0' encoding='utf-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Sample haml template
</title></head><body><div class="profile"><div class="left column"><div id="date">January 1, 2009
</div><div id="address">Richardson, TX
</div></div><div class="right column"><div id="email">tim@creationix.com
</div><div id="bio">Experienced software professional...

Note that this works almost the same as ruby's haml, but doesn't pretty print the html. This would greatly slow down and complicate the code. If you really want pretty printed html, then I suggest writing one using the xml parser library and process the resulting html..


Haml(haml) -> template(locals) -> html

This is the new (as of 0.2.0) way to generate haml templates. A haml template is a live function that takes in "this" context and a "locals" variable. This compile step takes a few milliseconds to complete so it should be done at startup and the resulting function should be cached. Then to use the template function you simply call it with the desired local variables and it will output html at blazing speeds (we're talking millions per second on my 13" MBP)

Compile and store a template:

var main = Haml(main_haml);

Then use it whenever you need a new version:

main({name: "Tim", age: 28});

That's it. Haml templating made easy!

If you want to store the generated javascript to a file to skip the compile step later on you can either decompile the template function or use the compile and optimize advanced functions directly.

Haml.compile(text) -> JavaScript compiled template

Given a haml template as raw text, this compiles it to a javascript expression that can later be eval'ed to get the final HTML.

The following input:

  = title
    %li Go Home
    %li Go Back

Produces the following JavaScript expression:

"<div id=\"home\">" + 
title +
"\n" + 
"<ul class=\"menu\">" + 
"<li>" + 
"Go Home\n" + 
"</li>" + 
"<li>" + 
"Go Back\n" + 
"</li>" + 
"</ul>" + 

Haml.optimize(js) -> optimized JavaScript expression

Takes the output of compile and optimizes it to run faster with the tradeoff of longer compile time. This is useful for framework developers wanting to use haml in their framework and want to cache the compiled templates for performance.

With the previous input it outputs:

"<div id=\"home\">" + 
title +
"\n<ul class=\"menu\"><li>Go Home\n</li><li>Go Back\n</li></ul></div>"

Notice how congruent static strings are merged into a single string literal when possible.

Haml.execute(js, context, locals) -> Executes a compiled template

Context is the value of this in the template, and locals is a hash of local variables.

Haml.render(text, options) -> html text

This is a convenience function that compiles and executes to html in one shot. Most casual users will want to use this function exclusively.

The text parameter is the haml source already read from a file.

The three recognized options are:

  • context: This is the this context within the haml template.
  • locals: This is an object that's used in the with scope. Basically it creates local variables and function accessible to the haml template.
  • optimize: This is a flag to tell the compiler to use the extra optimizations.

See test.js for an example usage of Haml.render

Executable JavaScript (not output)

New in version 0.2.6 is the ability to embed javascript in your template function. This lets you do variable assignments, if/else, switch statements, and even define functions. In Haml.js, execution blocks begin with a - and define a raw js block. This behaves slightly differently from Ruby's Haml. The advantage is that you can easily have multi-line executable blocks and comments, but the downside is that that you have to "outdent" the haml if you want to output from within a javascript block.

Simple example:

- var area = 0.5 * length * height
.area= area

Multi-line example:

- var obj = {
    area: 0.5 * b * h,
    r: opposite / adjacent
.triangle-details Area is: #{area} and the ratio is: #{r}

"Outdent" the haml in a javascript block (the "goodbye" div is not rendered!)

  - var a = "strings are truthy"
  - if(a){
  -  } else{
  - }

You can even define functions:

- function b(item){
  %b= item
  %span.length= item.length
- }
- b("Hi")
- b("World")

This outputs:

<div class="item"><b>Hi</b><span class="length">2</span></div><div class="item"><b>World</b><span class="length">5</span></div>

Please see test/raw_complex.haml for more details and examples.


Comments that will not appear in the compiled JS function nor the output begin with -#

-# This is a comment
- # This is a syntax error because of the extraneous space between the - and #.

If you want to have comments that will be in the compiled JS function but NOT the final HTML output:

- /*
  here we can have a comment that will not be output. Since executable-JS is block-level,
  we can have as much comment as we want, and it will not be output to html */

If you want an HTML comment that WILL be in the final HTML, begin with /


By default, Haml.js has no whitespace between tags. In this way, Haml.js is the opposite of Haml in Ruby. You can insert whitespace around or inside tags with > and <, respectively.

Most commonly, you want to have an a or span with whitespace around it:

Download the file
%a(href="/home")> here

Will produce:

Download the file <a href="/home">here</a> now.

You can also combine them if you want to have whitespace around and inside your tag.

%span<> This will have space in and around it.
%span>< This will, too.
%span><= "also works with code".toUpperCase()

Please see test/whitespace.haml for more examples.

Code interpolation

As of version 0.2.0 there is string interpolation throughout. This means that the body of regular text areas can have embedded code. This is true for attributes and the contents of plugins like javascript and markdown also. If you notice an area that doesn't support interpolation and it should then send me a note and I'll add it.

For interpolation, you may use #{} for escaped interpolation or !{} for unsafe interpolation.

Html Escaping / Santizer

You probably don't want to put unescaped user input right into your html. http://xkcd.com/327/ HTML/XSS sanitization is the new "Bobby Tables."

Let's assume we have a malicious username: name = "<script>...</script>"

Always unsafe:

  %span!= name

Always safe:

  %span&= name

Sometimes safe:

  %span= name

The behavior of = depends on the setting of the escapeHtmlByDefault configuration variable. To make = safe, call Haml like this:

  Haml(src, {escapeHtmlByDefault: true})


There are plugins in the parser for things like inline script tags, css blocks, and support for if statements and for loops.

:if statements

if statements evaluate a condition for truthiness (as opposed to a strict comparison to true) and includes the content inside the block if it's truthy.

:if todolist.length > 20
  %p Oh my, you are a busy fellow!

:each loops

:each loops allow you to loop over a collection including a block of content once for each item. You need to what variable to pull the data from and where to put the index and value. The index variable is optional and defaults to __key__.

Here is an example over a simple array.

  :each item in todolist
    %li= item.description

You can loop over the keys and values of objects too (Note the inner :each loop)

:each item in data
  :if item.age < 100
      :each name, value in item
        %dt&= name
        %dd&= value

:css and :script helpers.

It's easy to embed script and css tags in an haml document. Note that both :script and :javascript will work.

    function greet(message) {
      alert("Message from MCP: " + message);
  %title Script and Css test
    body {
      color: pink;
%body{ onload: "greet(\"I'm Pink\")" } COLOR ME PINK

This compiles to the following HTML:

<script type="text/javascript">
  function greet(message) {
    alert("Message from MCP: " + message);
<title>Script and Css test
<style type="text/css">
  body {
    color: pink;
</head><body onload="greet(&quot;I'm Pink&quot;)"> COLOR ME PINK

Custom Escaper

By default, Haml(src) returns a completely self-sufficient function, including a nested html_escape function. However, repeating the html_escape function definition in each of your templates is going to use more size than necessary. So, you may pass the name of a custom escaper in an optional config variable.

  Haml(src, {customEscape: "MyApp.esc"})

Then, the output template function definition will call MyApp.esc(string) and will omit the html_escape function definition. Haml.html_escape exposes the default escape function. If you are going to render your templates in the same context where you compile them (for instance, if you are only rendering them on the server side,) it might make sense to use Haml(src, {customEscape: "Haml.html_escape"})

Get Involved

If you want to use this project and something is missing then send me a message. I'm very busy and have several open source projects I manage. I'll contribute to this project as I have time, but if there is more interest for some particular aspect, I'll work on it a lot faster. Also you're welcome to fork this project and send me patches/pull-requests.

About Performance

The haml compiler isn't built for speed, it's built for maintainability. The actual generated templates, however are blazing fast. I benchmarked them with over 65 million renders per second on a small (20 line) template with some dynamic data on my laptop. Compare this to the 629 compiles per second I got out of the compiler. The idea is that you pre-compile your templates and reuse them on every request. While 629 per second is nothing compared to 65 million, that still means that your server with over 600 different views can boot up in about a second. I think that's fine for something that only happens every few weeks.


Haml-js is licensed under the MIT license.




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  • creationix
  • aaronblohowiak