In Javascript, when is this error thrown?

index.js

/**

 * Created by tushar.mathur on 24/12/15.

 */

'use strict'



const _ = require('lodash')

const Rx = require('rx')

const createDataStore = require('./src/createDataStore')



const fetch = x => Rx.Observable.fromPromise(window.fetch(x)) 

const parseJSON = x => Rx.Observable.fromPromise(x.json()) // Line: 11 (Where the exception is thrown)

var create = _.partial(createDataStore, fetch, parseJSON)

module.exports = {

  create,

  // Alias for legacy purposes

  createDataStore: create,

  createFetchStore: create

}

Is it a native promise error? What does it imply? Google shows no result found.