How to tell if an XMLHTTPRequest hit the browser cache

Question

If it possible to tell (within javascript execution) if a GET XMLHTTPRequest hit the browser cache instead of getting its response from the server?

Answer 1

When making an ajax request, You get the response code

if (request.readyState == 4) {
     if (request.status == 200) { // this number.
       ...

status 200 means you are getting a fresh copy of the data:

The request has succeeded. The information returned with the response is dependent on the method used in the request -

status 304 means the data has not changed and you will get it from the browser cache:

If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server SHOULD respond with this status code.

Read more on Status Code

Update:
You can add a cache buster to your URL to guarantee that you always hit the server:

var ajaxUrl = "/path?cache="+(Math.random()*1000000);