code: function getFile (str) {
    var ret = null
    var match = /[0-9]+,[0-9]+,.*/.test(str)
    if (!match) {
      return null
    }
    var a = str.split(',')
    if (a && a[2]) {
      ret = a[2]
      return ret
    } else {
      return null
    }
    if (isNaN(ret)) {
      return null
    }
    return ret
  }
docs: Get file of uri
  @param  {string} str The uri
  @return {string}     The file or null