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Javascript question

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So, I have two buttons, if I press first one it'll start endless cycle, if I press second one - it should break it.
Sound easy, but I encountered one problem which I have no idea how to solve.
I searched internet for this and I found that the problem is in flow, and I need multi-flows to solve this, and it easily can be done in c++ or c#. But js can have only one flow, and this option is not avaible for me.

I just want to know, is there any way to break cycles from outside in js?