Added note on triggered preflight when setting $.ajax contentType

[ksokhan]

When you define a specific contentType in an $.ajax request, jquery will send a CORS preflight OPTIONS request. This is somewhat "hidden" behaviour that can often cause headaches unless its documented.

[mgol]

Thanks for taking the time to contribute to the jQuery project! Can you sign the CLA?

Two issues:

1. Technically, this is not jQuery that triggers the OPTIONS request but the browser itself.
2. It's triggered only for cross-domain requests, not all of them.

[ksokhan]

@mzgol

• Signed CLA
• The wording I used simply says that a request is triggered, not specifically by jQuery. Despite this, end users of the documentation should still be told about any "leaky abstractions" that happen.
• Yes! Good point. Updated to say that this only occurs on cross-domain requests.

[ksokhan]

Is there anything more I can do to move this along?

[dmethvin]

Sometimes it takes a while for someone to review everything, sorry.

On this particular change, the use of passive voice in "will trigger a CORS preflight OPTIONS request" may lead someone to think that jQuery is doing this. That is what @mzgol was saying, since this is jQuery documentation the assumed actor is jQuery. With that in mind, I think the wording needs to make it clear that CORS requires this and the browser is doing it. Does that make sense? I do agree that preflight OPTIONS take many people by surprise though, so no objection from me regarding some sort of notice here.

[ksokhan]

@dmethvin thanks for breaking it down a bit more. I have revised the copy to be more clear on that point.

Didn't mean to sound impatient; I just wanted to help move things along.