Is caching in browser automatic?

Question

I have a JavaScript app that sends requests to REST API, the responses from server have cache headers (like ETag, cache-control, expires). Is caching of responses in browser automatic, or the app must implement some sort of mechanism to save the data?

Answer 1

An AJAX request is no different from a normal request - it's a GET/POST/HEAD/whatever request being sent by the browser, and it is handled as such. This is confirmed here:

The HTTP and Cache sub-systems of modern browsers are at a much lower level than Ajax’s XMLHttpRequest object. At this level, the browser doesn’t know or care about Ajax requests. It simply obeys the normal HTTP caching rules based on the response headers returned from the server.

As per the jQuery documentation, caches can also be invalidated in at least one usual way (appending a query string):

cache (default: true, false for dataType 'script' and 'jsonp')

Type: Boolean

If set to false, it will force requested pages not to be cached by the browser. Note: Setting cache to false will only work correctly with HEAD and GET requests. It works by appending "_={timestamp}" to the GET parameters. The parameter is not needed for other types of requests, except in IE8 when a POST is made to a URL that has already been requested by a GET.

So in short, given the same headers, AJAX responses are cached the same way as other requests.

Answer 2

Browser handles automatically cache of resources. What you seem to be asking about is the actuall response from the server.

You will need to set that up yourself in your application. You can do so both on front-end and backend.

Most of JS frameworks have cache control implemented, for example:

jQuery

$.ajaxSetup({
    // Disable caching of AJAX responses
    cache: false
});

AngularJS

$http.defaults.cache = false;

etc.

On backend it really depends on what language you using, what server engine etc.

Checkout Memcached for example http://memcached.org/

As with anything with web development there are odd things here and there, for example some IE versions are automatically chaching requests and you have to add unique id to the url to prevent that.