support es6 inside the config file

Since the latest releases of node support most ES6 features, I think there should be a way for users to use ES6 inside the karma.conf.js file. Gulp, for instance, allows it through the use of Babel.

[levithomason]

Gulp and webpack allow this by appending *.babel.js to their config files. They simply require('babel-core/register') for you before requiring their own config file.

I agree Karma should support this pattern. Node 4/5 are great, but do not support nearly as many future features as babel, such as import foo from 'foo'. Moreover, CommonJS modules are not fully compatible with ES6 modules. The export default statement in an ES6 module can be imported directly in another ES6 module. However, a CommonJS require(<some es6 module>) has to add .default to get the default export.

Since the Karma file is written in CommonJS (not future ES) the modules it require()s are beefed. You have to add CommonJS interop to use them, or add module.exports statements to your ES6 modules. Either case is a bit dirty and has consequences.

The ultimate fix IMHO is to support the babel register hook in the same fashion as gulp and webpack. In case that doesn’t make it in and others want to do this, you can do it yourself very easily:

karma.conf.js

require('babel-core/register');
module.exports = require('./karma.conf.babel').default;

karma.conf.babel.js

import AnES6Module from 'anywhere'

export default (config) => {
  config.set({...

Now, karma start karma.conf.js and it will require the babel hook, then require your es6 config file compiling with babel first. All your stuff will work.

EDIT For those interested, babel-plugin-add-module-exports is of help in this ^ venture. It adds the module exports for you.

[madnight]

"scripts": {
  "babel": "./node_modules/.bin/babel-node --presets es2015",
  "test": "NODE_ENV=test npm run babel -- ./node_modules/karma/bin/karma start karma.conf.babel.js"
}

^ this trick also works for me in case you only want one karma.conf file, instead of the two suggested by @levithomason solution