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August 27, 2015 13:03
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// Cache selectors | |
var lastId, | |
topMenu = $("#top-menu"), | |
topMenuHeight = topMenu.outerHeight()+15, | |
// All list items | |
menuItems = topMenu.find("a"), | |
// Anchors corresponding to menu items | |
scrollItems = menuItems.map(function(){ | |
var item = $($(this).attr("href")); | |
if (item.length) { return item; } | |
}); | |
// Bind to scroll | |
$(window).scroll(function(){ | |
// Get container scroll position | |
var fromTop = $(this).scrollTop()+topMenuHeight; | |
// Get id of current scroll item | |
var cur = scrollItems.map(function(){ | |
if ($(this).offset().top < fromTop) | |
return this; | |
}); | |
// Get the id of the current element | |
cur = cur[cur.length-1]; | |
var id = cur && cur.length ? cur[0].id : ""; | |
if (lastId !== id) { | |
lastId = id; | |
// Set/remove active class | |
menuItems | |
.parent().removeClass("active") | |
.end().filter("[href=#"+id+"]").parent().addClass("active"); | |
} | |
}); |
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