Javascript – jQuery has deprecated synchronous XMLHTTPRequest

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Like many others, my website is using jQuery. When I open the developer tools, I see a warning that says that XMLHTTPRequest is

deprecated because of its detrimental effects to the end user's experience.

I went on and read part of the documentation, but it was fairly technical. Can someone explain the consequences of shifting from XMLHTTPRequest to WHATWG in simple terms? It says it happened in 2012.

Also, the documentation says that Synchronous XMLHttpRequest outside of workers is in the process of being removed from the web platform, when that happens, if a user agent had them in a service, do they need to modify their existing code?

Best Answer

To avoid this warning, do not use:

async: false

in any of your $.ajax() calls. This is the only feature of XMLHttpRequest that's deprecated.

The default is async: true, so if you never use this option at all, your code should be safe if the feature is ever really removed.

However, it probably won't be -- it may be removed from the standards, but I'll bet browsers will continue to support it for many years. So if you really need synchronous AJAX for some reason, you can use async: false and just ignore the warnings. But there are good reasons why synchronous AJAX is considered poor style, so you should probably try to find a way to avoid it. And the people who wrote Flash applications probably never thought it would go away, either, but it's in the process of being phased out now.

Notice that the Fetch API that's replacing XMLHttpRequest does not even offer a synchronous option.

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