code: function easing(distance) {
    // t: current time, b: begInnIng value, c: change In value, d: duration
    var t = distance;
    var b = 0;
    var d = window.screen.availHeight; // 允许拖拽的最大距离
    var c = d / 2.5; // 提示标签最大有效拖拽距离
  
    return c * Math.sin(t / d * (Math.PI / 2)) + b;
  }
docs: 拖拽的缓动公式 - easeOutSine