Storage.js

var Storage = require('FuseJS/Storage');

function FileNotFoundError(message) {
  this.name = this.constructor.name;
  this.message = message || 'file could not be found';
  this.stack = (new Error()).stack;
}

FileNotFoundError.prototype = Object.create(Error.prototype);
FileNotFoundError.prototype.constructor = FileNotFoundError;

var tokens = {
  FILE_NOT_FOUND: 'File could not be found'
};

module.exports = {
  read: function (filename) {
    return new Promise(function (resolve, reject) {
      var failureHandler = function (err) {
        if (err === tokens.FILE_NOT_FOUND) {
          reject(new FileNotFoundError());
        }
      };

      Storage.read(filename)
             .then(resolve)
             .catch(failureHandler);
    });
  }
};