Facebook喜欢按钮回调

Question

When clicking a button like the 'like' button on Facebook, the like seems immediately (read: instantly) executed.

How is the user guaranteed that the Ajax call actually succeeded?
Is the 'like' visible at the client only executed as a response of the server?
Visually, it seems to happen instantly and I've never experienced it otherwise.

The response from the server after clicking 'like', looks like a bunch of code that I don't understand:

Answer 1

I read this question yesterday and then today Facebook's ajax failed!

Under a Facebook picture, the like button changed from "like" to "unlike", and then quickly changed back.

Then a dialog box box called "Try Again Soon" popped up, saying "Sorry there is a temporary problem with this post. Please try again in a few moments."

So that's what ensures the user won't just scroll past the error.