window.onload = function() {

var obtn = document.getElementById('btn');

var clientHeight = document.documentElement.clientHeight || document.body.clientHeight;

var timer = null;

var isTop = true;

window.onscroll = function() {

var osTop = document.documentElement.scrollTop || document.body.scrollTop;

if (osTop >= clientHeight) {

obtn.style.display = 'block';

} else {

obtn.style.display = 'none';

}

if (!isTop) {

clearInterval(timer);

}

isTop = false;

};

obtn.onclick = function() {

//设置定时器

timer = setInterval(function() {

var osTop = document.documentElement.scrollTop || document.body.scrollTop;

var ispeed = Math.floor(-osTop / 6);

document.documentElement.scrollTop = document.body.scrollTop = osTop + ispeed;

isTop = true;

console.log(osTop - ispeed);

if (osTop == 0) {

clearInterval(timer);

}

}, 30);

}

}

在onclick的方法中，修改了scrollTop的值不会触发onscroll事件吗？？？？事实上这段代码能运行成功。我不知道为什么不会，我觉得应该会呀。