JS如何實現輪播圖

本篇內容介紹了“JS如何實現輪播圖”的有關知識，在實際案例的操作過程中，不少人都會遇到這樣的困境，接下來就讓小編帶領大家學習一下如何處理這些情況吧！希望大家仔細閱讀，能夠學有所成！

實現功能：

1、自動輪播：鼠標停留在輪播圖上時不切換圖片，鼠標離開后自動輪播。

2、點擊左右按鈕切換圖片。

3、點擊下方按鈕切換到對應的圖片。

4、輪播圖大小自適應：

可以放入到執行的父容器中展示。

不指定父容器時，默認放入body標簽。占滿一屏的寬度，當改變瀏覽器窗口大小時，輪播圖大小成比例改變。

可以指定輪播圖的寬高。

實現方式：用面向對象的方式實現，使用時傳入圖片和圖片對應的數據，再創建實例。

import Carousel from './js/Carousel.js';
  var itemList1 = [{
                day: 26,
                date: "/Oct.2020",
                title: "秘境之藍 無阿里不西藏 自駕阿里小北線",
                src: "./carousel_img/a.jpg",
            },
            {
                day: 25,
                date: "/Oct.2020",
                title: "這是一個什么樣的國家？",
                src: "./carousel_img/b.jpg",
            },
            {
                day: 24,
                date: "/Oct.2020",
                title: "在徽州，給秋天寫了8封信",
                src: "./carousel_img/c.jpg",
            },
            {
                day: 23,
                date: "/Oct.2020",
                title: "「穿過狂野的風」趕赴內蒙的追羊計劃",
                src: "./carousel_img/d.jpg",
            },
            {
                day: 22,
                date: "/Oct.2020",
                title: "愛讓我們無所不能｜南極大冒險",
                src: "./carousel_img/e.jpg",
            },
        ];
        let carousel1 = new Carousel(itemList1);
        carousel1.appendTo(".div1");
        animation();
        function animation(){
            requestAnimationFrame(animation);
            carousel1.update();
            // carousel2.update();
}

代碼：

import Component from './Component.js';
 
export default class Carousel extends Component{
    
    imgList;
    bnList;
    imgCon;
    dot;
    dotList=[];
    data;
    direction;
    pos=0;
    x=0;
    speedX=1;
    bool=false;
    time=200;
    autoBool=true;
 
    // WIDTH=13.66;
    // HEIGHT=4.55;
    WIDTH;
    HEIGHT;
    
    constructor(_data,_width,_height){
        super("div");
        this.data=_data;
        this.width = _width;
        this.height = _height;
        this.elem.className = "carousel";
        // Object.assign(this.elem.style,{
        //     width:this.WIDTH+"rem",
        //     height:this.HEIGHT+"rem",
        //     position:"relative",
        //     overflow:"hidden",
        // });
        let arr = ["./carousel_img/left.png","./carousel_img/right.png"];
        let _imgList = this.data.reduce((value,item)=>{
            if(item.src) value.push(item.src);
            return value
        },arr);
        this.loadImg(_imgList,this.createCarousel);
        // window.addEventListener("resize",e=>this.resizeHandler(e));
    }
 
    createCarousel(imgList){
 
        Object.assign(this.elem.style,{
            width:this.WIDTH+"rem",
            height:this.HEIGHT+"rem",
            position:"relative",
            overflow:"hidden",
        });
 
        this.imgList = imgList;
        this.bnList = this.imgList.splice(0,2);
 
        imgList.forEach(item=>{
            Object.assign(item.style,{
                width:this.WIDTH+"rem",
                height:this.HEIGHT+"rem",
            })
        })
 
        this.createimgCon();
        this.createDotList();
        this.createBn();
        // 動畫一般在外面做，類里面只需要寫狀態更新即可。
        // this.animation();
 
        // 鼠標停留在輪播圖上時不進行自動輪播。
        this.elem.addEventListener("mouseenter",e=>this.mouseHandler(e));
        this.elem.addEventListener("mouseleave",e=>this.mouseHandler(e));
    }
    createimgCon(){
        this.imgCon = document.createElement("div");
        Object.assign(this.imgCon.style,{
            width:this.WIDTH*2+"rem",
            height:this.HEIGHT+"rem",
            position:"absolute",
        });
        let item = this.createItem(this.imgList[0],this.data[0]);
        this.imgCon.appendChild(item);
        this.elem.appendChild(this.imgCon);
    }
    createItem(img,obj){    
        let item = document.createElement("div");
        Object.assign(item.style,{
            width:this.WIDTH+"rem",
            height:this.HEIGHT+"rem",
            position:"relative",
            float:"left",
        });
        let title = document.createElement("div");
        Object.assign(title.style,{
            position:"absolute",
            left:"15%",
            top:"0.3rem",
            fontSize:"0.3rem",
            color:"#ffffff",
            textShadow:"0.02rem 0.02rem 0.02rem #000000",
            width:"8rem",
            lineHeight:"0.5rem",
        })
        let head1=document.createElement("div");
        Object.assign(head1.style,{
            height:"0.5rem",
        })
        head1.textContent = obj.date;
        let span = document.createElement("span");
        Object.assign(span.style,{
            fontSize:"0.4rem",
        });
        span.textContent = obj.day;
        let head2 = document.createElement("div");
        Object.assign(head2.style,{
            height:"0.5rem",
        })
        head2.textContent = obj.title;
        head1.insertBefore(span,head1.firstChild);
        title.appendChild(head1);
        title.appendChild(head2);
        item.appendChild(title);
        item.appendChild(img);
 
        return item;
    }
    createDotList(){
        this.dot = document.createElement("ul");
        Object.assign(this.dot.style,{
            listStyle:"none",
            margin:0,
            padding:0,
            position:"absolute",
            left:(this.WIDTH-1.8)/2+"rem",
            bottom:"0.3rem",            
        })
        for(let i=0;i<this.imgList.length;i++){
            let li = document.createElement("li");
            Object.assign(li.style,{
                width:"0.18rem",
                height:"0.18rem",
                borderRadius:"0.2rem",
                marginLeft:i===0?"0px":"0.2rem",
                border:"0.02rem solid red",
                float:"left",
            })
            this.dot.appendChild(li);
            this.dotList.push(li);
        }
        this.dot.addEventListener("click",e=>this.dotClickHandler(e));
        this.elem.appendChild(this.dot);
    }
    createBn(){
        for(let i=0;i<this.bnList.length;i++){
            Object.assign(this.bnList[i].style,{
                position:"absolute",
                top:(this.HEIGHT*100-this.bnList[i].height)/2/100+"rem",
            })
            if(i===0){
                this.bnList[i].style.left = "0.5rem";
            }else{
                this.bnList[i].style.right = "0.5rem";
            }
            this.bnList[i].addEventListener("click",e=>this.bnClickHandler(e));
            this.elem.appendChild(this.bnList[i]);
        }
    }
    bnClickHandler(e){
        if(this.bool) return
        if(e.target===this.bnList[0]){
            this.direction="left";
            this.pos++;
            if(this.pos>this.imgList.length-1) this.pos = 0;
        }else{
            this.direction="right";
            this.pos--;
            if(this.pos<0) this.pos=this.imgList.length-1;
        }
        this.bool=true;
        this.createNextItem();
    }
    dotClickHandler(e){
        if(e.target.constructor!==HTMLLIElement) return    //這里因為是對父元素進行偵聽，因此要先判斷點擊的是不是li，如果點擊的不是小圓點就不能改變開關，直接return。不能先改變開關。
        if(this.bool)return
        for(let i=0;i<this.dotList.length;i++){
            if(e.target===this.dotList[i]){
                if(this.pos===i) return
                this.direction=i<this.pos?"right":"left";
                this.pos=i;
            }
        }
        this.bool=true;
        this.createNextItem();
    }
    createNextItem(){
        let nextItem=this.createItem(this.imgList[this.pos],this.data[this.pos]);
        if(this.direction==="left"){
            this.imgCon.appendChild(nextItem);
            this.x=0;
        }else{
            this.imgCon.insertBefore(nextItem,this.imgCon.firstChild);
            this.x=-this.WIDTH;
        }
        this.imgCon.style.left=this.x+"rem";
    }
    update(){
        this.imgMove();
        this.autoPlay();
    }
    // 這里只需要做一個狀態更新即可。
    // 動畫在外面做。
    // animation(){
    //     requestAnimationFrame(this.animation);
    //     if(!this.bool) return
    //     this.imgMove();
    // }
    imgMove(){
        if(!this.bool) return
        if(this.direction==="left"){
            this.x-=this.speedX;
            if(this.x<-this.WIDTH){
                this.imgCon.firstElementChild.remove();
                this.x=0;
                this.bool=false;
            }
        }else{
            this.x+=this.speedX;
            if(this.x>0){
                this.imgCon.lastElementChild.remove();
                this.x=0;
                this.bool=false;
            }
        }
        this.imgCon.style.left=this.x+"rem";
    }
    autoPlay(){
        if(!this.autoBool) return
        this.time--;    //增加防抖
        if(this.time===0){   
            let evt = new Event("click");
            this.bnList[0].dispatchEvent(evt);
            this.time=200;
        }
    }
    resizeHandler(e){
        document.documentElement.style.fontSize=document.documentElement.clientWidth/(this.WIDTH*100)*100+"px";
    }
    appendTo(parent){
        if(typeof parent==="string") parent = document.querySelector(parent);
        parent.appendChild(this.elem);
        if(!isNaN(this.WIDTH) && !isNaN(this.HEIGHT)) return
        if(parent===document.body){
            this.WIDTH = 13.66;
            this.HEIGHT = 4.55;
        }else{
            let rect = parent.getBoundingClientRect();
            this.WIDTH=rect.width/100;
            this.HEIGHT=rect.height/100;
        }
    }
    mouseHandler(e){
        if(e.type==="mouseenter"){
            this.autoBool=false;
        }else{
            this.autoBool=true;
        }
    }
 
    // 圖片預加載
    loadImg(_imgList,_callBack){
        let img = new Image();
        img.i=0;
        img.arr=[];
        img.imgList=_imgList;
        // img.callBack=_callBack;
        img.src=_imgList[img.i];
        img.addEventListener("load",e=>this.imgLoadFinishHandler(e));
    }
    imgLoadFinishHandler(e){
        // console.log(e.currentTarget);
        e.currentTarget.arr.push(e.currentTarget.cloneNode());
        e.currentTarget.i++;
        if(e.currentTarget.i<e.currentTarget.imgList.length){
            e.currentTarget.src = e.currentTarget.imgList[e.currentTarget.i];
        }else{
            // e.currentTarget.callBack(e.currentTarget.arr);
            this.createCarousel(e.currentTarget.arr);
        }
    }
}

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