mousedown / mouseup is the only way to get notification of middle button interactions, so detecting a down-down event without an intermediate mouseout event mouseout more or less the best you can do. It's not very good.
I would not worry, because even if you are trapped in this possibility, there are many other interactions that you cannot pick up. As well as the middle click (which may not be βOpen on a new tab in all browsers / configurations, for example, in IE6, which will be enabled by the user in scroll mode), the user can right-click andβ Open in a new window β, or drag the link to the address bar or a new tab or other other browser-related actions to navigate.
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