es2015/migration/RecordFetcher.js
function fetchAllRecords(transaction, objectStores) {
  return PromiseSync.all(objectStores.map((descriptor) => {
    return fetchRecords(
      transaction.getObjectStore(descriptor.objectStore),
      descriptor.preprocessor
    )
  })).then((fetchedRecords) => {
    let recordsMap = {}
    
    for (let i = 0; i < objectStores.length; i++) {
      recordsMap[objectStores[i].objectStore] = fetchedRecords[i]
    }
    
    return recordsMap
  })
}
function fetchAllRecords(transaction, objectStores) {
  return PromiseSync.all(objectStores.map((descriptor) => {
    return fetchRecords(
      transaction.getObjectStore(descriptor.objectStore),
      descriptor.preprocessor
    )
  })).then((fetchedRecords) => {
    let recordsMap = {}
    
    for (let i = 0; i < objectStores.length; i++) {
      recordsMap[objectStores[i].objectStore] = fetchedRecords[i]
    }
    
    return recordsMap
  })
}
function fetchAllRecords ( transaction , objectStores ) { return PromiseSync . all ( objectStores . map ( ( descriptor ) => { return fetchRecords ( transaction . getObjectStore ( descriptor . objectStore ) , descriptor . preprocessor ) } ) ) . then ( ( fetchedRecords ) => { let recordsMap = { } for ( let i = 0 ; i < objectStores . length ; i ++ ) { recordsMap [ objectStores [ i ] . objectStore ] = fetchedRecords [ i ] } return recordsMap } ) }
Fetches all records from the specified object stores using the provided
read-write transaction.

@param {Transaction} transaction The read-write transaction to use to access
the object stores.
@param {(string|{objectStore: string, preprocessor: function(*, (number|string|Date|Array)): (*|UpgradedDatabaseSchema.SKIP_RECORD|UpgradedDatabaseSchema.DELETE_RECORD)=})[]} objectStores
The names of object stores that should have their records fetch or
(possibly partially filled) object store fetch descriptors, mixed in
an array.
@return {PromiseSync<Object<string, {key: (number|string|Date|Array), record: *}[]>>}
A promise that resolves once all the records have been fetched and
the records marked for deletion were deleted.
The promise resolves to a map of object store names to the records
fetched from the object store, except for the records marked for
skipping or deletion.
Fetches all records from the specified object stores using the provided read - write transaction .