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This is meant to be a very simple asset compiler that helps speed up development. You add it as middleware in your development environment and it will compile and host all of your assets. This is not recommmended for use during production and it doesn't help you compile your assets for production- not the Rails asset pipeline.

hosting bootstrap

In this example we have a less file assets/css/style.less on disk that uses bootstrap. When the client requests assets/css/style.css the asset compiler compiles assets/css/style.less and serves the result.

var flatiron = require('flatiron'),
    union = require('union'),
    assetCompiler = require('asset-compiler'),
    app =;
app.use(flatiron.plugins.http, {
  before: [
    assetCompiler.middleware(__dirname, {
      css: ['/assets/css', '/vendor/bootstrap/less']

adding a compiler (not complete)

Compilers are defined by creating an object that maps file extensions to compilers. For example, css might map to a less compiler and a stylus compiler. The example below shows how you would define a less compiler.

var less = require('less'),
    _ = require('underscore');
var getCompilerMap = function(root, assets) {
  return {
    css: {
      less: function(body, cb) {
        var parser = new less.Parser({
          paths:, function(path) { return root + path; })
        return parser.parse(body, function(e, tree) {
          if (e) {
          cb(null, tree.toCSS());

I plan to make it easy to override and add new compilers, but the functionality isn't quite there yet. If you add it feel free to submit a pull request.