Should I use JSON or AJAX for response data?

You are perhaps a little confused.

JSON and AJAX are not an either-or choice.

JSON and XML is a choice.

JSON and AJAX are distinct and largely unrelated, although AJAX often uses JSON, it can just easily use XML, HTML or plain text.

Or are you referring to the X in AJAX (XML)? If so, the arguments for JSON are basically:

• JSON has a smaller payload than equivalent XML; and
• JSON is easier to deal with in Javascript (compare eval'ing a JSON object to walking an XML fragment).

Other than that, it's largely personal preference.

JSON is just a data-interchange format. It describes in what way the data is represented during transmission. You can not replace Ajax with JSON.

Ajax stands for Asynchronous JavaScript and XML, but when using JSON you could say that you're using AJAJ (Asynchronous JavaScript and JSON).

Maybe you are thinking of the jQuery methods $.getJSON() and $.get()?

The difference is that $.getJSON() automatically assumes that it's JSON data, while $.get() will just fetch the data as plain text.

When using $.getJSON() you're also able to fetch data between domains.