SQA Testing: async callback javascript test

I am newbie to test automation. I came cross this question a couple of times in a different flavor. First one is: A method returns the values in random order to a list. Now I have to write a test to assert values in the list are correct. Second one is: There is javascript async call back method that returns chunks of data. How do I test completeness of this data is correct? I may need to write a test script to test this one. I am not sure if these both questions are similar in nature, but I like to know the answers or guidance to refer to. Appreciate help.