使用：getElementViewTop($(".product .tab a")[0])  //注意一定要加[0]

//有滚动条得情况下，求标签离浏览器视口高度

function getElementViewTop(element) {

var actualTop = element.offsetTop;

var current = element.offsetParent;

var elementScrollTop;

while (current !== null) {

actualTop += current.offsetTop;

current = current.offsetParent;

}

elementScrollTop = document.documentElement.scrollTop || window.pageYOffset || document.body.scrollTop;

return actualTop - elementScrollTop;

}