Problem
1. Explain the two characteristics of Ajax that help it achieve its goals.
2. Explain why the callback function is written as an anonymous function in the request phase function.
3. Modify the example application of Section 10.2 to have it provide the addresses of repeat customers, using a hash of names and addresses.
4. Modify the example application of Section 10.2 to have it validate the zip code when it is entered, to ensure that it is a valid zip code for the given city and state. The response document can be a PHP script that looks up the zip code and the city and state in a small table of examples.