code: function isJsFile(file) {
      "use strict";
      var ext = fileExt(file);
      var valid = Object.keys(require.extensions).map(function(val) {
          return val.replace(/^\./, '');
      }).filter(function(ext) {
          return ext === 'js' || ext === 'coffee';
      });
      return isString(ext, "string") && valid.indexOf(ext) !== -1;
  }
docs: Checks if a file is apparently javascript compatible (.js or .coffee).
  
  @param  String  file  Path to the file to test
  @return Boolean