var scrollTop = ...寫在定時(shí)器里面

都有g(shù)etter和setter你取值是取出來(lái)了值。setter才是修改實(shí)際內(nèi)容。你對(duì)你的變量修改跟原有的setter沒關(guān)系。

const realScroll = [
  [document.body, 'scrollTop'],
  [window, 'pageYOffset'],
  [document.documentElement, 'scrollTop']
];
const len = realScroll.length;
let time = setInterval(function() {
  let i = 0,
      getter = function() {
        return realScroll[i][0][realScroll[i][1]];
      },
      setter = function(v) {
        realScroll[i][0][realScroll[i][1]] = v;
      },
      top;
  for (; i < len; i++) {
    top = getter();
    if (top) {
      setter(top - 200);
      if (top <= 0) {
        clearInterval(time);
      }
    }
  }
});

 function scroll() {
            return {
                top: window.pageYOffset || document.documentElement.scrollTop,
                left: window.pageXOffset || document.documentElement.scrollLeft
            }
        }

scroll().top