第四片叶子's 博客

Back to top link’s purpose is to quickly position the viewport back to a beginning of a web page. Sometimes you have a variable height of the content and this link is unnecessary if a particular page is shorter than viewport height. With this simple JavaScript, you can hide it depending on page’s height. See the example web site示范效果.
var d = document; onload = function() {     var viewport_height = (self.innerHeight) ? self.innerHeight : (document.documentElement && document.documentElement.clientHeight) ? document.documentElement.clientHeight : (document.body) ? document.body.clientHeight : 0;     var page_height = d.getElementsByTagName('body')[0].offsetHeight;     var ttl = d.getElementById('to_top_link');     if (page_height < viewport_height) ttl.style.visibility = 'hidden'; };

原文地址：http://www.maratz.com/blog/archives/2006/05/22/smart-back-to-top-link/

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