“回到顶部”代码简单封装

原文链接：完美实现一个“回到顶部”

简单封装

/**
* 缓冲函数
* @param {Number} position 当前滚动位置
* @param {Number} destination 目标位置
* @param {Number} rate 缓动率
* @param {Function} callback 缓动结束回调函数 两个参数分别是当前位置和是否结束
*/
var easeout = function (position, destination, rate, callback) {
  if (position === destination || typeof destination !== 'number') {
    return false;
  }
  destination = destination || 0;
  rate = rate || 2;

  // 不存在原生`requestAnimationFrame`，用`setTimeout`模拟替代
  if (!window.requestAnimationFrame) {
    window.requestAnimationFrame = function (fn) {
      return setTimeout(fn, 17);
    }
  }

  var step = function () {
    position = position + (destination - position) / rate;
    if (Math.abs(destination - position) < 1) {
      callback(destination, true);
      return;
    }
    callback(position, false);
    requestAnimationFrame(step);
  };
  step();
}

调用

var scrollTopSmooth = function (position) {
  // 当前滚动高度
  var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
  easeout(scrollTop, position, 5, function (val) {
    window.scrollTo(0, val);
  });
}

$backToTop = document.querySelector('.back-to-top')
$backToTop.addEventListener('click', function () {
  scrollTopSmooth(200);
}, false);

效果查看戳scrollIntoView.html