页面锚点跳转JS缓冲特效

* Smooth scrolling
Changes links that link to other parts of this page to scroll
smoothly to those links rather than jump to them directly, which
can be a little disorienting.
sil, http://www.kryogenix.org/
v1.0 2003-11-11
v1.1 2005-06-16 wrap it up in an object
*/
var ss = {
fixAllLinks: function() {
// Get a list of all links in the page
var allLinks = document.getElementsByTagName('a');
// Walk through the list
for (var i=0;i<allLinks.length;i++) {
var lnk = allLinks[i];
if ((lnk.href && lnk.href.indexOf('#') != -1) &&
( (lnk.pathname == location.pathname) ||
('/'+lnk.pathname == location.pathname) ) &&
(lnk.search == location.search)) {
// If the link is internal to the page (begins in #)
// then attach the smoothScroll function as an onclick
// event handler
ss.addEvent(lnk,'click',ss.smoothScroll);
}
}
},
smoothScroll: function(e) {
// This is an event handler; get the clicked on element,
// in a cross-browser fashion
if (window.event) {
target = window.event.srcElement;
} else if (e) {
target = e.target;
} else return;
// Make sure that the target is an element, not a text node
// within an element
if (target.nodeName.toLowerCase() != 'a') {
target = target.parentNode;
}
// Paranoia; check this is an A tag
if (target.nodeName.toLowerCase() != 'a') return;
// Find the <a name> tag corresponding to this href
// First strip off the hash (first character)
anchor = target.hash.substr(1);
// Now loop all A tags until we find one with that name
var allLinks = document.getElementsByTagName('a');
var destinationLink = null;
for (var i=0;i<allLinks.length;i++) {
var lnk = allLinks[i];
if (lnk.name && (lnk.name == anchor)) {
destinationLink = lnk;
break;
}
}
if (!destinationLink) destinationLink = document.getElementById(anchor);
// If we didn't find a destination, give up and let the browser do
// its thing
if (!destinationLink) return true;
// Find the destination's position
var destx = destinationLink.offsetLeft;
var desty = destinationLink.offsetTop;
var thisNode = destinationLink;
while (thisNode.offsetParent &&
(thisNode.offsetParent != document.body)) {
thisNode = thisNode.offsetParent;
destx += thisNode.offsetLeft;
desty += thisNode.offsetTop;
}
// Stop any current scrolling
clearInterval(ss.INTERVAL);
cypos = ss.getCurrentYPos();
ss_stepsize = parseInt((desty-cypos)/ss.STEPS);
ss.INTERVAL =setInterval('ss.scrollWindow('+ss_stepsize+','+desty+',"'+anchor+'")',10);
// And stop the actual click happening
if (window.event) {
window.event.cancelBubble = true;
window.event.returnValue = false;
}
if (e && e.preventDefault && e.stopPropagation) {
e.preventDefault();
e.stopPropagation();
}
},
scrollWindow: function(scramount,dest,anchor) {
wascypos = ss.getCurrentYPos();
isAbove = (wascypos < dest);
window.scrollTo(0,wascypos + scramount);
iscypos = ss.getCurrentYPos();
isAboveNow = (iscypos < dest);
if ((isAbove != isAboveNow) || (wascypos == iscypos)) {
// if we've just scrolled past the destination, or
// we haven't moved from the last scroll (i.e., we're at the
// bottom of the page) then scroll exactly to the link
window.scrollTo(0,dest);
// cancel the repeating timer
clearInterval(ss.INTERVAL);
// and jump to the link directly so the URL's right
location.hash = anchor;
}
},
getCurrentYPos: function() {
if (document.body && document.body.scrollTop)
return document.body.scrollTop;
if (document.documentElement && document.documentElement.scrollTop)
return document.documentElement.scrollTop;
if (window.pageYOffset)
return window.pageYOffset;
return 0;
},
addEvent: function(elm, evType, fn, useCapture) {
// addEvent and removeEvent
// cross-browser event handling for IE5+,  NS6 and Mozilla
// By Scott Andrew
if (elm.addEventListener){
elm.addEventListener(evType, fn, useCapture);
return true;
} else if (elm.attachEvent){
var r = elm.attachEvent("on"+evType, fn);
return r;
} else {
alert("Handler could not be removed");
}
}
}
ss.STEPS = 100;  //设置滑动速度
ss.addEvent(window,"load",ss.fixAllLinks);