超好用的移动端布局自适应大小rem判断js文件及超过一定高度回到顶部按钮代码

//以下代码放到一个adapt.js文件当中
(function (doc, win) {
var docEl = doc.documentElement,
resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
recalc = function () {
var clientWidth = docEl.clientWidth;
if (!clientWidth) return;
docEl.style.fontSize = 20 * (clientWidth /750) + 'px';
};

if (!doc.addEventListener) return;
win.addEventListener(resizeEvt, recalc, false);
doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);

function goTopEx() {
var obj = document.getElementById("goTopBtn");
function getScrollTop() {
return document.documentElement.scrollTop + document.body.scrollTop;
}
function setScrollTop(value) {
if (document.documentElement.scrollTop) {
document.documentElement.scrollTop = value;
} else {
document.body.scrollTop = value;
}
}
window.onscroll = function() {
getScrollTop() > 0 ? obj.style.display = "": obj.style.display = "none";
}
obj.onclick = function() {
var goTop = setInterval(scrollMove, 10);
function scrollMove() {
setScrollTop(getScrollTop() / 1.1);
if (getScrollTop() < 1) clearInterval(goTop);
}
}
}

<script src="js/adapt.js"></script>
<-- 以下是超过高度显示回到顶部代码 -->
<div id="goTopBtn"><img src="img/index_03.png"/></div>
<script type=text/javascript>goTopEx();</script>