I would like to write a JavaScript function that validates a zip code, by checking if the zip code actually exists. Here is a list of all zip codes:

http://www.census.gov/tiger/tms/gazetteer/zips.txt (I only care about the 2nd column)

This is really a compression problem. I would like to do this for fun. OK, now that's out of the way, here is a list of optimizations over a straight hashtable that I can think of, feel free to add anything I have not thought of:

• Break zipcode into 2 parts, first 2 digits and last 3 digits.
• Make a giant if-else statement first checking the first 2 digits, then checking ranges within the last 3 digits.
• Or, covert the zips into hex, and see if I can do the same thing using smaller groups.
• Find out if within the range of all valid zip codes there are more valid zip codes vs invalid zip codes. Write the above code targeting the smaller group.
• Break up the hash into separate files, and load them via Ajax as user types in the zipcode. So perhaps break into 2 parts, first for first 2 digits, second for last 3.

Lastly, I plan to generate the JavaScript files using another program, not by hand.

Edit: performance matters here. I do want to use this, if it doesn't suck. Performance of the JavaScript code execution + download time.

Edit 2: JavaScript only solutions please. I don't have access to the application server, plus, that would make this into a whole other problem =)