Allow jQuery.ajax.settings.beforeSend to handle async promises

[pensierinmusica]

Hi,

Currently jQuery.ajax.settings.beforeSend only works with sync code. It would be nice if it could support async code too.

Let's look at a code example. Imagine I need the value of foo to be added to all jQuery Ajax request headers in my app.

$.ajaxSetup({
  beforeSend: function (req) {
    if (localStorage.foo) {
      // Sync version - "foo" is locally available
      req.setRequestHeader('foo', localStorage.foo);
    } else {
      // Async version - "foo" needs to be fetched from an API server
      return $.get({
        url: '/foo',
        beforeSend: null
      })
        .done(function (data) {
          localStorage.foo = data;
          req.setRequestHeader('foo', data);
        });
    }
  }
});

As the web is moving more and more to async operations, imho it would make sense to support this pattern in jQuery. Thoughts?

Thanks!

[markelog]

See #2532 (comment)

Sorry

[dmethvin]

This doesn't need to be done (and IMO shouldn't be done) inside $.ajax(), just create your memoizing function and call that. Using $.ajaxSetup() is definitely a bad idea unless you have written and understand every ajax call that will be made through these new semantics.

[pensierinmusica]

unless you have written and understand every ajax call that will be made through these new semantics.

@dmethvin, yep, that's exactly the case at hand. Anyways, this is what I ended up doing, although I wish jQuery Ajax could provide a better / async way to handle these situations:

http://stackoverflow.com/questions/32643469/jquery-how-to-make-ajaxsend-wait-for-another-ajax-response-before-proceeding

Cheers