zepto返回顶部动画

点击返回顶部

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();
  });

zepto滚动到某个位置

$.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;
};