JavaScript仿小米轮播图效果

本文是自己仿写的小米轮播图的写法，通过透明度改变进行轮播的，新手，写的可能不是很好，有啥不合理的情况，望提出，指正，全部的代码放最下面
有很多写法重复，有空的时候，我把重复的代码封装一下

关于透明度渐变的动画效果

比如 delayOpacity(OliArray[pre],0,-0.1); 就是将OliArray[pre]这个对象的透明度转换成0，速度为0.1

function delayOpacity(obj,target,speed){
        clearInterval(timer);
        timer = setInterval(function(){
            var old = getComputedStyle(obj,null)['opacity']; 
            var newVal = +old + +speed;//+是将字符串转变成number类型
            if(parseInt(speed)>0 && newVal>=target){
                newVal = 1;
            }
            if(parseInt(speed)<0 && newVal<=target){
                newVal = 0;
            }
            obj.style.opacity = newVal;//每次将新的值赋值给该对象的透明度，产生渐变效果
            if(newVal==target){
                clearInterval(timer);//当透明度的值和目标中的透明度的值一样的时候，将定时器关闭
            }
        },100);
    }

关于自动轮播的方法

我的轮播有四张，但是写了五张图片，第五张和第一张图片是一样的，目的是为了透明度转换的比较合理，不会突然从最后一张变到第一张
全局变量 next代表轮播图将要切换的那一张，pre代表轮播图目前的这张

function autoPlay(){
        autoTimer = setInterval(function(){
            next++;
            pre++;
            next %= OliArray.length;
            pre %= OliArray.length;
            if(pre==OliArray.length-1){
                pre = 0;
            }
            for(let i=0;i<OliArray.length;i++){
                if(i!=next){
                    OliArray[i].style.zIndex = 0;
                    /*解决点击前几张图片时，之后自动轮播没有切换效果的问题，
                    由于后面的图片显示的效果在前面的图片之上,所以如果在播放到第三张图片时，
                    点击第一张图片后，自动轮播时，因为第三张图片的显示在第二张图片之上
                    所以从第一张到第二张，是没有动画效果，且图片一直停在第三张
                    所以要把将要显示的图片的层级设置为1，其他图片的层级设置为0*/
                }
                if(i!=pre)
                    OliArray[i].style.opacity = 0;
                if(i!=OliArray.length-1){
                    PointerArray[i].className = ""; //这个是点击时，除点击的那个原点外，其他的激活的样式清空
                }
            }
            OliArray[next].style.zIndex=1;
            delayOpacity(OliArray[pre],0,-0.1);//将上一张的透明度由1变成0
            delayOpacity(OliArray[next],1,0.1);//将要显示的图片的透明度由0变成1
            if(next==OliArray.length-1) {
                next = 0;
                OliArray[next].style.opacity = 1;//到最后一张图片的时候，立即切换到第一张，相对于假装轮播到第一张了，因为用户的眼睛没有那么亮
            }
            PointerArray[next].className = "active";
        },3000);
    }

关于点击上一张图片

prevBanner.onclick = function(){
        //将自动轮播的定时器清空
        clearInterval(autoTimer);
        pre = next;//此时的pre就是原来切换到的那张图片 
        next = next-1>=0? next-1:OliArray.length-2;//next就是上一张,要切换的图片
        for(let i=0;i<OliArray.length;i++){
            if(i!=next){
                OliArray[i].style.zIndex = 0;
            }
            if(i!=pre)
                OliArray[i].style.opacity = 0;
            if(i!=OliArray.length-1){
                PointerArray[i].className = "";
            }
        }
        OliArray[next].style.zIndex = 1;
        delayOpacity(OliArray[pre],0,-0.1);
        delayOpacity(OliArray[next],1,0.1);
        if(next==OliArray.length-1) {
            next = 0;
            OliArray[next].style.opacity = 1;
        }
        PointerArray[next].className = "active";
        pre = next - 1;
        //开启自动轮播
        autoPlay();
    }

关于点击下一张

和自动轮播有点像，但是没有定时器（这里我觉得可以封装函数来写，以后改一下）

nextBanner.onclick = function(){
        //将自动轮播的定时器清空
        clearInterval(autoTimer);
        next++;
        pre++;
        next %= OliArray.length;
        pre %= OliArray.length;
        if(pre==OliArray.length-1){
            pre = 0;
        }
        for(let i=0;i<OliArray.length;i++){
            if(i!=next){
                OliArray[i].style.zIndex = 0;
            }
            if(i!=pre)
                OliArray[i].style.opacity = 0;
            if(i!=OliArray.length-1){
                PointerArray[i].className = "";
            }
        }
        OliArray[next].style.zIndex = 1;
        delayOpacity(OliArray[pre],0,-0.1);
        delayOpacity(OliArray[next],1,0.1);
        if(next==OliArray.length-1) {
            next = 0;
            OliArray[next].style.opacity = 1;
        }
        PointerArray[next].className = "active";
        //开启自动轮播
        autoPlay();
    }

关于点击某个原点，切换到该原点的图片

for(let i=0;i<PointerArray.length;i++){
        PointerArray[i].onclick = function(){
            //将自动轮播的定时器清空
            clearInterval(autoTimer);
            for(let j=0;j<OliArray.length;j++){
                if(j!=i){
                    OliArray[j].style.zIndex = 0;
                }
                if(j!=next)
                    OliArray[j].style.opacity = 0;
                if(j!=OliArray.length-1){
                    PointerArray[j].className = "";
                }
            }
            OliArray[i].style.zIndex=1;
            delayOpacity(OliArray[next],0,-0.1);
            delayOpacity(OliArray[i],1,0.1);
            PointerArray[i].className = "active";
            pre = i - 1 == 0? OliArray.length-1:i-1;
            next = i;
            //开启自动轮播
            autoPlay();
        }
    }

html部分

<div class="banner-wapper">
        <div class="container">
            <div class="banner">
                <ul class="img-list">
                    <li>
                        <a href="#">
                            <img src="./img/1.jpg" alt="">
                        </a>
                    </li>
                    <li>
                        <a href="#">
                            <img src="./img/2.jpg" alt="">
                        </a>
                    </li>
                    <li>
                        <a href="#">
                            <img src="./img/3.jpg" alt="">
                        </a>
                    </li>
                    <li>
                        <a href="#">
                            <img src="./img/4.jpg" alt="">
                        </a>
                    </li>
                    <li>
                        <a href="#">
                            <img src="./img/1.jpg" alt="">
                        </a>
                    </li>
                </ul>
                <div class="pointer">
                    <a href="javascript:;"></a>
                    <a href="javascript:;"></a>
                    <a href="javascript:;"></a>
                    <a href="javascript:;"></a>
                </div>
                <div class="prev-next">
                    <a class="prev" href="javascript:;"></a>
                    <a class="next" href="javascript:;"></a>
                </div>
            </div>
        </div>
</div>

CSS部分

.banner{
    position: relative;
    height: 460px;
}
.banner .img-list li{
    position: absolute;
    opacity: 0;
}
.banner-wapper .banner a img{
    width: 1226px;
    height: 460px;
    vertical-align: top;
}
.banner .img-list li:nth-child(1){
    opacity: 1;
}
.pointer{
    z-index: 2;
    position: absolute;
    right: 30px;
    bottom: 20px;
}
.pointer a{
    float: left;
    width: 6px;
    height: 6px;
    border: 2px rgba(255, 255, 255, 0.4) solid;
    box-sizing: content-box;
    margin: 0 4px;
    border-radius: 50%;
    background: rgba(0, 0, 0, 0.4);
}
.pointer a:hover,
.pointer .active{
    border-color:rgba(0, 0, 0, 0.4);
    background-color: rgba(255, 255, 255, 0.4);
}
.prev-next a{
    width: 41px;
    height: 69px;
    position: absolute;
    top: 0;
    bottom: 0;
    margin: auto 0;
    background-image: url(../img/icon-slides.png);
}
.prev-next .prev{
    z-index: 2;
    left: 234px;
    background-position: -84px 50%;
}
.prev-next .prev:hover{
    background-position: 0 0;
}
.prev-next .next{
    z-index: 2;
    right: 0;
    background-position: -125px 50%;
}
.prev-next .next:hover{
    background-position: -42px 50%;
}

js部分

window.onload = function(){
    var Oul = document.getElementsByClassName("img-list")[0];
    var OliArray = Oul.getElementsByTagName("li");
    var pointer = document.getElementsByClassName("pointer")[0];
    var PointerArray = pointer.getElementsByTagName("a");
    var nextBanner = document.getElementsByClassName("next")[0];
    var prevBanner = document.getElementsByClassName("prev")[0];

    var timer,autoTimer, next = 0,pre = OliArray.length-1;
    PointerArray[0].className = "active";
    
    autoPlay();
    // 点击轮播
    for(let i=0;i<PointerArray.length;i++){
        PointerArray[i].onclick = function(){
            //将自动轮播的定时器清空
            clearInterval(autoTimer);
            for(let j=0;j<OliArray.length;j++){
                if(j!=i){
                    OliArray[j].style.zIndex = 0;
                }
                if(j!=next)
                    OliArray[j].style.opacity = 0;
                if(j!=OliArray.length-1){
                    PointerArray[j].className = "";
                }
            }
            // console.log(pre,next,i)
            OliArray[i].style.zIndex=1;
            delayOpacity(OliArray[next],0,-0.1);
            delayOpacity(OliArray[i],1,0.1);
            PointerArray[i].className = "active";
            pre = i - 1 == 0? OliArray.length-1:i-1;
            next = i;
            //开启自动轮播
            autoPlay();
        }
    }

    // 点击下一张
    nextBanner.onclick = function(){
        //将自动轮播的定时器清空
        clearInterval(autoTimer);
        next++;
        pre++;
        next %= OliArray.length;
        pre %= OliArray.length;
        if(pre==OliArray.length-1){
            pre = 0;
        }
        for(let i=0;i<OliArray.length;i++){
            if(i!=next){
                OliArray[i].style.zIndex = 0;
            }
            if(i!=pre)
                OliArray[i].style.opacity = 0;
            if(i!=OliArray.length-1){
                PointerArray[i].className = "";
            }
        }
        OliArray[next].style.zIndex = 1;
        delayOpacity(OliArray[pre],0,-0.1);
        delayOpacity(OliArray[next],1,0.1);
        if(next==OliArray.length-1) {
            next = 0;
            OliArray[next].style.opacity = 1;
        }
        PointerArray[next].className = "active";
        //开启自动轮播
        autoPlay();
    }
    //点击上一张
    prevBanner.onclick = function(){
        //将自动轮播的定时器清空
        clearInterval(autoTimer);
        pre = next;
        next = next-1>=0? next-1:OliArray.length-2;
        for(let i=0;i<OliArray.length;i++){
            if(i!=next){
                OliArray[i].style.zIndex = 0;
            }
            if(i!=pre)
                OliArray[i].style.opacity = 0;
            if(i!=OliArray.length-1){
                PointerArray[i].className = "";
            }
        }
        OliArray[next].style.zIndex = 1;
        delayOpacity(OliArray[pre],0,-0.1);
        delayOpacity(OliArray[next],1,0.1);
        if(next==OliArray.length-1) {
            next = 0;
            OliArray[next].style.opacity = 1;
        }
        PointerArray[next].className = "active";
        pre = next - 1;
        //开启自动轮播
        autoPlay();
    }

    // 自动轮播
    function autoPlay(){
        autoTimer = setInterval(function(){
            next++;
            pre++;
            next %= OliArray.length;
            pre %= OliArray.length;
            if(pre==OliArray.length-1){
                pre = 0;
            }
            for(let i=0;i<OliArray.length;i++){
                if(i!=next){
                    OliArray[i].style.zIndex = 0;
                }
                if(i!=pre)
                    OliArray[i].style.opacity = 0;
                if(i!=OliArray.length-1){
                    PointerArray[i].className = "";
                }
            }
            OliArray[next].style.zIndex=1;
            delayOpacity(OliArray[pre],0,-0.1);
            delayOpacity(OliArray[next],1,0.1);
            if(next==OliArray.length-1) {
                next = 0;
                OliArray[next].style.opacity = 1;
            }
            PointerArray[next].className = "active";
        },3000);
    }
    function delayOpacity(obj,target,speed){
        clearInterval(timer);
        timer = setInterval(function(){
            var old = getComputedStyle(obj,null)['opacity'];
            // console.log(getComputedStyle(obj,null)['opacity'])
            var newVal = +old + +speed;
            // console.log(obj,newVal)
            if(parseInt(speed)>0 && newVal>=target){
                newVal = 1;
            }
            if(parseInt(speed)<0 && newVal<=target){
                newVal = 0;
            }
            obj.style.opacity = newVal;
            // console.log(getComputedStyle(obj,null)['opacity'])
            if(newVal==target){
                clearInterval(timer);
            }
        },100);
    }
}

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