title: Karma Invalid config file
body: <p>In order to make karma config file easier to configure path, I am using variable to store certain part of the path.</p>
  
  <pre><code>var publicfolder = "public"
  var mypath = "packages/vendor/package/";
  
  files: [
    publicfolder+'/assets/libs/jquery/dist/jquery.js',
    publicfolder+'/assets/libs/angular/angular.js',
    publicfolder+'/assets/libs/**/*.js',
    publicfolder+'/app/**/*.js',
    mypath +'/public/app/**/*.test.js',
    mypath +'/public/app/**/*.html'
  ],
  
  preprocessors: {
      mypath +'/public/app/**/*.html':['ng-html2js']
  },
  </code></pre>
  
  <p>However, when I run the test, it come into the error saying </p>
  
  <pre><code>E:\www\project\karma.conf.js:83
      mypath +'/public/app/**/*.html':['ng-html2js']
             ^
  ERROR [config]: Invalid config file!
    SyntaxError: Unexpected token +
      at Module._compile (module.js:439:25)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
  </code></pre>
  
  <p>My question is WHY? Why I can't put variable there? Why is that it is fine to put it in the <code>files</code> array but not in the <code>preprocessors</code>?</p>