If you are returning a json value use json to read that.
See http://api.jquery.com/jQuery.getJSON/
http://pinoytech.org/blog/post/How-to-Use-JSON-with-jQuery-AJAX
Here is an example to read json value
$('document').ready(function(){
$('#submit).click(function(){
$.post('your_php_page.php', {employee_id: '456'},
function(data){
console.log(data.first_name);
console.log(data.last_name);
}, 'json');
})
});
Hope it helps