Day26--课后作业（广告图片自动播放）

CSS代码：

<style type="text/css">
                *{  
                    margin: 0;
                    padding: 0;
                    position: relative;
                }
                #div1{  
                    display: flex;
                    align-items: flex-end;
                    justify-content: center;
                    width: 940px;
                    height: 430px;
                    margin: auto;
                    background-color: lightblue;
                    background: url("img/1.jpg");
                    
                }
                #ul1{
                    list-style: none;
                    font-size: 40px;
                    color: red;
                    display: flex;
                    width: 100px;
                    height: 50px;
                    justify-content: space-around;
                }
             #ul1 li{
                    cursor: pointer;
                }
            </style>

html代码如下：

<div id="div1">
            <div id="div2">
                <ul id="ul1">
                    <li id="list1">■</li>
                    <li id="list2">■</li>
                    <li id="list3">■</li>
                    <li id="list4">■</li>
                </ul>
            </div>  
        </div>

JS代码如下：

<script type="text/javascript">
            var index=0;
            var listId=["list1","list2","list3","list4"];
            var image=["url(img/1.jpg)","url(img/2.jpg)","url(img/3.jpg)","url(img/4.jpg)"];
            var div=document.querySelector("#div1");
            div.addEventListener('mouseover',stopShow);
            div.addEventListener('mouseout',startShow);
            var timeId;
            var temp;
            startShow();
            
            function startShow(){
                timeId=window.setInterval(function(){
                    index %= image.length;
                    document.querySelector("#div1").style.backgroundImage=image[index];
                    changeListStyle(index);
                    index+=1;
                },2000);
                
            } 
            function stopShow(){
                window.clearInterval(timeId);
            }           
            function changeListStyle(index){
                var listStyle=document.querySelector("#"+listId[index]);
                listStyle.style.color="greenyellow";
                temp=["list1","list2","list3","list4"];
                temp.splice(index,1);
                console.log(temp);
                for(i=0 ;i<temp.length;i+=1){
                    var listStyleOther=document.querySelector("#"+temp[i]);
                    listStyleOther.style.color="red";
                }
                }
            
            var listLi=document.querySelectorAll("li");
            for (i=0;i<listLi.length;i+=1){
                listLi[i].addEventListener("mouseover",function(evt){
                    var singlelist=evt.target||evt.srcElement;
                    index=listId.indexOf(singlelist.id);
                    document.querySelector("#div1").style.backgroundImage=image[index];
                    changeListStyle(index);
                })
            }
            
            
        </script>

效果：

QQ截图20181106203114.png
QQ截图20181106203125.png

说明
1、整体采用flex的方式进行CSS布局，弹性盒子模型灵活多变，易于得到理想的布局；
2、index是整体程序的关键，控制index就控制了div背景图和li标签内容的显示状态；
3、抽离出changeListStyle函数作为控制Li标签内容color变化的函数，其中temp是用于将非index选中的Li标签内容变为统一的颜色；temp在循环不断的被改变，应该有垃圾回收机制将未引用的对象清理；