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Preprocessor to compile CoffeeScript on the fly.


The easiest way is to keep karma-coffee-preprocessor as a devDependency. You can simple do it by:

npm install karma-coffee-preprocessor --save-dev


Following code shows the default configuration

// karma.conf.js 
module.exports = function(config) {
    preprocessors: {
      '**/*.coffee': ['coffee']
    coffeePreprocessor: {
      // options passed to the coffee compiler 
      options: {
        bare: true,
        sourceMap: false
      // transforming the filenames 
      transformPath: function(path) {
        return path.replace(/\.coffee$/, '.js')
    // make sure to include the .coffee files not the compiled .js files 
    files: [

If you set the sourceMap coffee compiler option to true then the generated source map will be inlined as a data-uri.

For more information on Karma see the homepage.