Download file via ajax. Copied from here http://stackoverflow.com/a/23797348

gistfile1.js

module.exports = downloadAjaxFile

function downloadAjaxFile (xhr) {
  /* jshint maxcomplexity: 7 */
  var filename = ''
    , disposition = xhr.getResponseHeader('Content-Disposition')

  if (disposition && disposition.indexOf('attachment') !== -1) {
    var filenameRegex = /filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/
      , matches = filenameRegex.exec(disposition)

    if (matches != null && matches[1]) filename = matches[1].replace(/['"]/g, '')
  }

  var type = xhr.getResponseHeader('Content-Type')
    , blob = new Blob([ xhr.responseText ], { type: type })

  // IE workaround for "HTML7007: One or more blob URLs were revoked by
  // closing the blob for which they were created. These URLs will no
  // longer resolve as the data backing the URL has been freed.
  if (typeof window.navigator.msSaveBlob !== 'undefined') return window.navigator.msSaveBlob(blob, filename)

  var URL = window.URL || window.webkitURL
    , downloadUrl = URL.createObjectURL(blob)

  if (filename) {
    // use HTML5 a[download] attribute to specify filename
    var a = document.createElement('a')
    // safari doesn't support this yet
    if (typeof a.download === 'undefined') {
      window.location = downloadUrl
    } else {
      a.href = downloadUrl
      a.download = filename
      document.body.appendChild(a)
      a.click()
    }
  } else {
    window.location = downloadUrl
  }

  setTimeout(function () { URL.revokeObjectURL(downloadUrl); }, 100)
}