function goTop(acceleration, time) {acceleration = acceleration || 0.1;time = time || 16;var x1 = 0;var y1 = 0;var x2 = 0;var y2 = 0;var x3 = 0;var y3 = 0;if (document.documentElement) {x1 = document.documentElement.scrollLeft || 0;y1 = document.documentElement.scrollTop || 0;}if (document.body) {x2 = document.body.scrollLeft || 0;y2 = document.body.scrollTop || 0;}var x3 = window.scrollX || 0;var y3 = window.scrollY || 0;// 滚动条到页面顶部的水平距离var x = Math.max(x1, Math.max(x2, x3));// 滚动条到页面顶部的垂直距离var y = Math.max(y1, Math.max(y2, y3));// 滚动距离 = 目前距离 / 速度, 因为距离原来越小, 速度是大于 1 的数, 所以滚动距离会越来越小var speed = 1 + acceleration;window.scrollTo(Math.floor(x / speed), Math.floor(y / speed));// 如果距离不为零, 继续调用迭代本函数if (x > 0 || y > 0) {var invokeFunction = "goTop(" + acceleration + ", " + time + ")";window.setTimeout(invokeFunction, time);}}$("#back2top").on("click", function() {//$("body").scrollTop(0);//window.scrollTo(0,0);
    goTop();});

$.fn.scrollTo = function(options) {var defaults = {toT: 0, //滚动目标位置durTime: 500, //过渡动画时间delay: 30, //定时器时间callback: null //回调函数
  };var opts = $.extend(defaults, options),timer = null,_this = this,curTop = _this.scrollTop(), //滚动条当前的位置subTop = opts.toT - curTop, //滚动条目标位置和当前位置的差值index = 0,dur = Math.round(opts.durTime / opts.delay),smoothScroll = function(t) {index++;var per = Math.round(subTop / dur);if (index >= dur) {_this.scrollTop(t);window.clearInterval(timer);if (opts.callback && typeof opts.callback == 'function') {opts.callback();}return;} else {_this.scrollTop(curTop + index * per);}};timer = window.setInterval(function() {smoothScroll(opts.toT);}, opts.delay);return _this;
};