This is a HORRIBLE change!  Do you realize how many sites rely on async = false??  This is a necessary thing to use when you don't want the user to be triggering other scripts (i.e. by clicking on a screen button) while waiting for a response.

You guys seriously need to rethink deprecating this!  Best practices aside, it should be up to the developer whether or not to piss off users by freezing the screen until code is executed.  Developers will still do this, the only difference is that it's going to be a pain in the ass to accomplish what is now very easy to do by using async = false.

PLEASE RECONSIDER!


http://xhr.spec.whatwg.org/#sync-warning

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Developers must not pass false for the async argument when the JavaScript global environment is a document environment as it has detrimental effects to the end user's experience. User agents are strongly encouraged to warn about such usage in developer tools and may experiment with throwing an "InvalidAccessError" exception when it occurs so the feature can eventually be removed from the platform. 
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