JavaScript: Reliably detect which mouse button was pressed

How do you reliably detect which mouse button -- the left, right, middle, or a combination of them -- the user pressed while doing, say, a drag and drop operation?

The properties most tutorials will tell you are the button or which properties on the event object. They're both unreliable.

In this video, I demonstrate their unreliability and then code up a reliable solution.

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Video clip played at the end of this tutorial:

Sanskrit Song | Anandamayi | MADE OF BLISS
Singer: Gaiea

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