原生JS實現(xiàn) MUI導航欄透明漸變效果

body,p,h1{margin: 0;}
.module-layer{
 width: 100%;
 position: fixed;
 top: 0;
 left: 0;
 z-index: 100000;
}
.module-layer-content{
 position: relative;
 min-width: 320px;
 max-width: 750px;
 width: 100%;
 margin: 0 auto;
 background-color: rgba(255, 0, 0, 0.9);
}
.module-layer-bg{
 width: 100%;
 height: 100%;
 background: #000;
 opacity: .7;
 position: absolute;
 top: 0;
 left: 0;
 z-index: -1;
}
.layer-head-name{
 height: 50px;
 line-height: 50px;
 text-align: center;
 padding: 0 50px;
 font-size: 20px;
}
.layer-return,.layer-share{
 width: 50px;
 height: 50px;
 line-height: 50px;
 text-align: center;
 position: absolute;
 top:0;
 z-index: 1;
}
.layer-return{left: 0;}
.layer-share{right: 0;}
.fixed-layer{
 height: 100%;
 display: none;
 z-index: 100001;
}
.relative-layer{height: 100%;}
.layer-content{
 padding:3%;
 position: relative;
 top: 20%;
}
.layer-close{
 width: 2rem;
 height: 2rem;
 position: absolute;
 top:3%;
 right: 3%;
}
.pr {
 position:relative;
}
#shop-input::-webkit-input-placeholder {
 color:#fff;
}
#shop-input:-moz-placeholder {
 color:#fff;
}
#shop-input::-moz-placeholder {
 color:#fff;
}
#shop-input:-ms-input-placeholder {
 color:#fff;
}
#shop-input {
 border:none;
 outline:none;
 background:transparent;
}
.search-box {
 height:30px;
 border-radius:20px;
 top:10px;
 overflow:hidden;
 z-index:10;
}
.search-box:after {
 content:'';
 display:block;
 width:100%;
 height:30px;
 background:#fff;
 opacity:.5;
 position:absolute;
 top:0;
 left:0px;
 z-index:-1;
}
#shop-input {
 height:28px;
 line-height:28px;
 font-size:16px;
 position:absolute;
 top:0;
 left:30px;
}
.shop-search {
 width:16px;
 height:16px;
 position:absolute;
 top:7px;
 left:6px;
}
.layer-return{
 background: url(images/return.png) no-repeat center center/12px 20px;
}
.layer-share{
 background: url(images/share.png) no-repeat center center/20px 30px;
}
a {
 -webkit-tap-highlight-color: transparent;
 -webkit-touch-callout: none;
 -webkit-user-select: none;
}
.module-content{
 min-width: 320px;
 max-width: 750px;
 width: 100%;
 margin: 0 auto;
 background: #fff;
}
.module-content div:first-child img{margin-top: 0;}
.module-content div img{
 display: block;
 width: 100%;
 margin-top: 10px;
}

<header class="module-layer">
 <div class="module-layer-content">
 <p class="layer-return"></p>
 <h1 class="layer-head-name">
 <div class="pr search-box">
 <img class="shop-search" src="images/search.png"/>
 <input id="shop-input" type="text" placeholder="搜索店內(nèi)商品" value="" />
 </div>
 </h1>
 <p class="layer-share"></p>
 </div>
</header>
<div class="module-content">
 <div><img src="images/banner.png"/></div> 
 <div><img src="images/banner1.png"/></div> 
 <div><img src="images/banner3.png"/></div>
 <div><img src="images/banner4.jpg"/></div>
 <div><img src="images/banner5.png"/></div>
 <div><img src="images/banner6.png"/></div>
 <div><img src="images/banner7.jpg"/></div>
 <div><img src="images/banner8.jpg"/></div>
</div>

(function(){
 //獲取滾動條當前位置
 function getScrollTop(){ 
 　　var scrollTop = 0, bodyScrollTop = 0, documentScrollTop = 0; 
 　　if(document.body){ 
 　　　　bodyScrollTop = document.body.scrollTop; 
 　　} 
 　　if(document.documentElement){ 
 　　　　documentScrollTop = document.documentElement.scrollTop; 
 　　} 
 　　scrollTop = (bodyScrollTop - documentScrollTop > 0) ? bodyScrollTop : documentScrollTop; 
 　　return scrollTop; 
 }
 //獲取CSS樣式
 function getStyle(element, attr){
 if(element.currentStyle){
 return element.currentStyle[attr];
 }else{
 return window.getComputedStyle(element,null)[attr];
 }
 }
 //獲取原始backgroundColor值
 var color = getStyle(document.getElementsByClassName('module-layer-content')[0],'backgroundColor');
 //取到RGB
 var colorRgb = color.substring(0,color.lastIndexOf(',') + 1);
 //取到A
 var colorA = color.substring(color.lastIndexOf(',') + 1,color.length - 1);
 //對A判斷，如果最終值小于0.9，直接設置為1
 if(colorA < 0.9){colorA = 1;}
 //設置背景色的A的函數(shù)
 var setCoverOpacity = function() {
 document.getElementsByClassName('module-layer-content')[0].style.background = colorRgb + (((getScrollTop() / 550) > colorA) ? colorA : (getScrollTop() / 550)) + ')';
 }
 //初始化函數(shù)
 setCoverOpacity();
 //綁定滾動監(jiān)聽事件
 window.addEventListener('scroll',setCoverOpacity,false);
}())