https://github.com/caolan/async#seriestasks-callback

Async.series passes a 2 param callback to the functions in the array, the first parameter is an error, the second is a result status, I am always calling back with null for both since I am doing my own error handling and don't care about the array of results since I am logging them to the console as I go.

The syntax in the example above will show what I am doing.

The checks will not interleave since the next method in the async series array will not be called until the previous has called back.