The original item passed to the operation function.
OptionaloutputThe result property will be undefined if the promise is rejected when operating on the item.
OptionalrejectedThe value of the promise rejection (often an Error object, but can technically be anything).
Items can be skipped if the RunParallelOptions.shouldSkipFunc is used and evaluated to true for an item, or if
RunParallelOptions.onlyFirstN was passed and the item was not in range.
Set to true if not skipped, the promise wasn't rejected and the success evaluation function returned true for the output, false otherwise.
The result from an individual operation during a call to runParallel.