为什么这个 jQuery.ajax 不会引发错误？

Question

We had an interesting issue this morning - the details of the issue itself aren't relevant here, and I already fixed it, but I did run into something strange, to me, about jQuery.

The site I am building internally runs on https, only, so Apache is set to redirect any inbound http request to its https equivalent. This redirect is working fine. But, I had a bug in my software where I was trying to send the following ajax request:

jQuery.ajax({  type:       "PUT",
           url:        "http://somewhere.com/cmdt/todo_lists/8457/toggle",
           data:       { deployment_id: 827},
           dataType:   "script"});

I understand that this would fail - I'm alright with jQuery not wanting to follow a redirect. But the actual behaviour is even weirder: I never see an xhr request go out at all, And there's no javascript error. It just fails, silently, If I change the url to https, or to a relative path. it works fine, no problem? My question is? why wasn't it TRYING to send out the request before? And why didn't it raise an error?

Answer 1

The reason you're not getting a failure is because it's a cross-site request, and so instead of using XMLHttpRequest , it's actually generating an HTML <script> tag and dropping it into the DOM, and using that mechanism to load the file.

This works reasonably well (considering it's a complete hack around wrong-headed browser "security" notions) but there's no way for jQuery to trap errors at that point, sadly. You will likely get a browser error if you have developer mode turned on, but that's it.

Answer 2

If you run that from an url that's https and try to open the equivalent http page you run into cross domain problems due to the different protocols they use. Have a look at same origin policy .