only register scroll event handler if necessary (expensive in IE) #44
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If the scroll event handler is always attached, even with the scroll-detection related features disabled (
extendPage: false, scrollHistory:false, showAndHideOnScroll: false, highlightOnScroll: false
), there is a notable lag in IE due to performance issues with jQuery'sscrollTop()
(http://stackoverflow.com/a/5001300).This code change simply wraps the registration of the event handler in a check so that it is only registered if one of the relevant options is enabled to avoid wasting resources in a handler that ends up doing no work.