Turn javascript object into a string

use json2.js from http://www.JSON.org/json2.js

e.g.
<script src="json2.js"></script>
...
JSON.stringify( {
    FirstName: $('#FirstName').val(),
    LastName: $('#LastName').val()
});

To turn a JSON string into javascript ojbect, use parseJSON.

var json = '{"fname" : "john", "lname" : "smith", "age" : 35}';
var jsObject = $.parseJSON(json);