Successful parsing requires that the order of the data must be maintained. That being said, it is trivial to convert this format into one that maintains the same attribute names as the first JSON format:

parseJSON.js

function parseJSON(responseText) {
 var users = [];
 var usersArray = eval('(' + responseText + ')');
 for (var i = 0, len = usersArray.length; i < len; i++) {
 users[i] = {
 id: usersArray[i][0],
 username: usersArray[i][1],
 realname: usersArray[i][2],
 email: usersArray[i][3]
 };
 }
 return users;
}