旋转木马幻灯片切换效果JS源码详解

首先，放上慕课网的课程链接，源码是在这个课程里分享出来的，https://www.imooc.com/learn/386。

文章适合学习过这个课程的同学，再看这篇文章，可能有更深入的理解。主要是对各种this,$(this),self等的指代，这里只对js文件进行了注释，需要其它css文件以及html文件的，请到官网下载

最先看得部分应该是Carousel.init的方法，然后再从上往下看

;(function($){

    var Carousel = function(poster){
            //console.log(poster);由于一直不清楚这里poster和this的区别，所以我把他们打印出来了，poster就是下面init方法里面new Carousel的时候传进来的
            //console.log(this); this指代的是Carousel{}
            var self = this;
            //保存单个旋转木马对象
            this.poster                  = poster;    //把poster的值传递给当前对象this的poster属性，值传递
            this.posterItemMain = poster.find("ul.poster-list");
            this.nextBtn               = poster.find("div.poster-next-btn");
            this.prevBtn               = poster.find("div.poster-prev-btn");
            this.posterItems        =poster.find("li.poster-item");
            if(this.posterItems.size()%2==0){
                this.posterItemMain.append(this.posterItems.eq(0).clone());
                this.posterItems = this.posterItemMain.children();
            };
            this.posterFirstItem  = this.posterItems.first();
            this.posterLastItem  = this.posterItems.last();
            this.rotateFlag   = true;
            //默认配置参数
            this.setting = {
                                    "width":1000,            //幻灯片的宽度
                                    "height":270,                //幻灯片的高度
                                    "posterWidth":640,    //幻灯片第一帧的宽度
                                    "posterHeight":270,    //幻灯片第一帧的高度
                                    "scale":0.9,                    //记录显示比例关系
                                    "speed":500,
                                    "autoPlay":false,
                                    "delay":5000,
                                    "verticalAlign":"middle" //top bottom
                                    };
            $.extend(this.setting,this.getSetting()); //把自定义的配置与默认配置合并，如果自定义配置了相同的参数，将会覆盖默认的参数，否则会保留默认参数
            
            //设置配置参数值
            this.setSettingValue();
            this.setPosterPos();
            //左旋转按钮
            this.nextBtn .click(function(){
                if(self.rotateFlag){
                    self.rotateFlag = false; 
                    self.carouseRotate("left"); //这里不能再用this.rotate();因为这里的this是button这个dom节点，所以我们要在上面保存self
                };
            });
            //右旋转按钮
            this.prevBtn .click(function(){
                if(self.rotateFlag){
                    self.rotateFlag = false;
                    self.carouseRotate("right");
                };
            });
        //是否开启自动播放
        if(this.setting.autoPlay){
            this.autoPlay();
            this.poster.hover(function(){
                                        window.clearInterval(self.timer);
                                        },function(){
                                        self.autoPlay();
                                        });
            
        };

    };
    Carousel.prototype = {  //完全重写了prototype为一个对象实例，不明白的可以百度一下“prototype完全重写”
        autoPlay:function(){
            var self = this;
            this.timer = window.setInterval(function(){
                self.nextBtn.click();
            },this.setting.delay);

        },

        //旋转
        carouseRotate:function(dir){
            var _this_  = this;
            var zIndexArr = [];
            //左旋转
            if(dir === "left"){
                this.posterItems .each(function(){
                    var self = $(this),
                           prev = self.prev().get(0)?self.prev():_this_.posterLastItem,
                           width = prev.width(),
                           height =prev.height(),
                           zIndex = prev.css("zIndex"),
                           opacity = prev.css("opacity"),
                           left = prev.css("left"),
                           top = prev.css("top");
                            zIndexArr.push(zIndex);    
                           self.animate({
                                                   width,
                                                height:height,
                                                //zIndex:zIndex,
                                                opacity:opacity,
                                                left:left,
                                                top:top
                                                },_this_.setting.speed,function(){
                                                    _this_.rotateFlag = true;
                                                });
                });
                //zIndex需要单独保存再设置，防止循环时候设置再取的时候值永远是最后一个的zindex
                this.posterItems.each(function(i){
                    $(this).css("zIndex",zIndexArr[i]);
                });
            }else if(dir === "right"){//右旋转
                this.posterItems .each(function(){
                    var self = $(this),
                           next = self.next().get(0)?self.next():_this_.posterFirstItem,
                           width = next.width(),
                           height =next.height(),
                           zIndex = next.css("zIndex"),
                           opacity = next.css("opacity"),
                           left = next.css("left"),
                           top = next.css("top");
                           zIndexArr.push(zIndex);    
                           self.animate({
                                                   width,
                                                height:height,
                                                //zIndex:zIndex,
                                                opacity:opacity,
                                                left:left,
                                                top:top
                                                },_this_.setting.speed,function(){
                                                    _this_.rotateFlag = true;
                                                });
    
                });
                //zIndex需要单独保存再设置，防止循环时候设置再取的时候值永远是最后一个的zindex
                this.posterItems.each(function(i){
                    $(this).css("zIndex",zIndexArr[i]);
                });
            };
        },
        //设置剩余的帧的位置关系
        setPosterPos:function(){
                var   self = this;
                var     sliceItems  = this.posterItems.slice(1),
                        sliceSize     = sliceItems.size()/2,
                        rightSlice   = sliceItems.slice(0,sliceSize),
                        level            = Math.floor(this.posterItems.size()/2),
                        leftSlice      =sliceItems.slice(sliceSize);
            
                //设置右边帧的位置关系和宽度高度top
                var rw = this.setting.posterWidth,
                       rh  = this.setting.posterHeight,
                       gap = ((this.setting.width-this.setting.posterWidth)/2)/level;
                
                var firstLeft = (this.setting.width-this.setting.posterWidth)/2;
                var fixOffsetLeft = firstLeft+rw;
                //设置左边位置关系
                rightSlice.each(function(i){
                    level--;
                    rw = rw *self.setting.scale;
                    rh = rh *self.setting.scale
                    var j = i;
                    $(this).css({
                                        zIndex:level,
                                        rw,
                                        height:rh,
                                        opacity:1/(++j),
                                        left:fixOffsetLeft+(++i)*gap-rw,
                                        top:self.setVerticalAlign(rh)
                                        });
                });
                //设置左边的位置关系
                var lw = rightSlice.last().width(),
                       lh  =rightSlice.last().height(),
                       oloop = Math.floor(this.posterItems.size()/2);
                leftSlice.each(function(i){
                    $(this).css({
                                        zIndex:i,
                                        lw,
                                        height:lh,
                                        opacity:1/oloop,
                                        left:i*gap,
                                        top:self.setVerticalAlign(lh)
                                        });
                    lw = lw/self.setting.scale;
                    lh = lh/self.setting.scale;
                    oloop--;
                });
        },
        //设置垂直排列对齐
        setVerticalAlign:function(height){
            var verticalType  = this.setting.verticalAlign,
                    top = 0;
            if(verticalType === "middle"){
                top = (this.setting.height-height)/2;
            }else if(verticalType === "top"){
                top = 0;
            }else if(verticalType === "bottom"){
                top = this.setting.height-height;
            }else{
                top = (this.setting.height-height)/2;
            };
            return top;
        },
        //设置配置参数值去控制基本的宽度高度。。。
        setSettingValue:function(){
            this.poster.css({
                                        this.setting.width,
                                        height:this.setting.height
                                    });
            this.posterItemMain.css({
                                        this.setting.width,
                                        height:this.setting.height
                                    });
            //计算上下切换按钮的宽度
            var w = (this.setting.width-this.setting.posterWidth)/2;
            //设置切换按钮的宽高，层级关系
            this.nextBtn.css({
                                        w,
                                        height:this.setting.height,
                                        zIndex:Math.ceil(this.posterItems.size()/2)
                                        });
            this.prevBtn.css({
                                        w,
                                        height:this.setting.height,
                                        zIndex:Math.ceil(this.posterItems.size()/2)
                                        });
            
            this.posterFirstItem.css({
                                        this.setting.posterWidth,
                                        height:this.setting.posterHeight,
                                        left:w,
                                        top:0,
                                        zIndex:Math.floor(this.posterItems.size()/2)
                                        });
        },
        //获取人工配置参数
        getSetting:function(){
            
            var setting = this.poster.attr("data-setting");
            if(setting&&setting!=""){
                return $.parseJSON(setting);
            }else{
                return {};
            };
        }
    
    };
    Carousel.init = function(posters){ //为Carousel添加方法init,传入一个posters List作为参数
        var _this_ = this;  //既然是为Carousel添加的方法，那么这里的this就是指代Carousel对象，可以打印出来看效果
        posters.each(function(){//遍历poster List参数，遍历出来的是每一个poster HTML DOM
            new  _this_($(this));//把每一个遍历出来的 poster HTML DOM 对象变成jQuery对象，再new 新的Carousel对象出来，这样页面上各个轮播区域就会互不相关，并且new出来的对象拥有了Carousel对象所拥有的所有属性和方法，所以能实现轮播效果(变成jQuery对象主要是为了接下来的用jQuery的方法，first()之类的)
        });
    };
    window["Carousel"] = Carousel; 
})(jQuery);