Defaults to 10 - the maximum number of tasks that will be allowed to run concurrently. While NodeJS is single-threaded, it is worth controlling the number of running tasks to avoid overwhelming I/O or an external service.
OptionalonlyIf provided, this will limit processing to the first N items. Useful for testing new functionality on a subset of items.
Note that this will completely bypass any processing of items after the first N items. So for example, there won't be "skipped" items for those not processed - they simply won't be on the result object at all.
OptionalshouldIf provided, this will be used to determine whether or not an item should be skipped.
Additional options that can be passed to runParallel.