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What technology/framework is StackOverflow using to asynchronously update clients?

As I've observed, if I've opened the same question in two or more tabs, and up/down vote a question/answer - its effect is seen on both the tabs.

I'm a beginner at JavaScript and am still stumbling upon new things. This (synchronising of votes and other aspects across tabs) in particular seems to be very useful thing to learn. How are they achieving this feat?

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