js图片如何加载效果 具体实例代码如下

.picList{

  img{

    width:100px;

    height:100px;

    position:relative;

    /*加载失败时显示灰底文字*/

    &:after{

      content:"( ⊙ o ⊙ )加载失败";

      font-size:6px;

      font-family: FontAwesome;

      color:rgb(100,100,100);

      display: flex;

      justify-content:center;

      align-items:center;

      position:absolute;

      top:0;

      left:0;

      width:100px;

      height:100px;

      background-color:#ddd;

    }

  }

}

.lazy{

  background:url(../pic/loading.gif)centerno-repeat;

  border:1pxsolidblack;

}

#loadBar{

  width:200px;

  height:15px;

  background: linear-gradient(90deg,#187103,#81b50b,#187103);

  border:10pxsolidwhite;

  position:absolute;

  top:150px;

  left:50%;

  margin-left:-100px;

  #loadBarMask{

    width:70%;//这个数值显示没有加载成功的图片

    height:100%;

    background-color: beige;

    position:absolute;

    right:0;

  }

}

varlazyPic = $('img.lazy');

varloadBarMask = $('#loadBarMask');

varpicList = $('.picList');

varactivePic = 0;

vartotalPic = lazyPic.length;

/*每秒加载一张图片*/

functionloadPicPerSecond(){

  lazyPic.each(function(index){

    varself = $(this);

    //console.log(self[0].complete);

    /*img标签已经事先写在html中，所以此时的complete状态全部都是true*/

    setTimeout(function(){

      src[index] = self.attr('data-src');

      self.attr('src',src[index]);

      self.removeClass('lazy');

      //图片获得正确src地址之后，可以执行下面的onload操作

      self[0].onload =function(){

        //加载读条loadBar动画

        countPic();

      }

      //图片获得的src地址不正确时，执行下面的onerror操作

      self[0].onerror =function(){

        /*this.style.background = 'url(pic/compressed/picList18.jpg) center no-repeat'*/

        countPic();

      }

    },1000*index);

  })

}

/*根据onload的执行情况来计算当前的图片加载进度.每onload一次，activePic就增加1*/

functioncountPic(){

  activePic++;

  varleftPic = totalPic - activePic;

  varpercentPic = Math.ceil(leftPic/totalPic*100);//没有加载的图片百分比，和loadBarMask的宽度占比配合

  console.log("已加载"+(100-percentPic)+"%");

  loadBarMask.css("width",percentPic+"%");

  if(percentPic==0){

    $('#loadBar').hide();

  }

}

varlazyPic = $('img.lazy');

varloadBarMask = $('#loadBarMask');

varpicList = $('.picList');

varscrollTop,

  clientHeight,

  scrollHeight;

varthreshold = 200;//最后一张图片距离窗口200px的时候开始加载图片

varsrc = [];

varactivePic = 0;

vartotalPic = lazyPic.length;

//待加载的图片数据

vardirtSrc ="pic/compressed/picList";

varpicData = {imgSrc:[

  dirtSrc +"20.jpg",

  dirtSrc +"21.jpg",

  dirtSrc +"22.jpg",

  dirtSrc +"23.jpg",

  dirtSrc +"24.jpg",

  dirtSrc +"25.jpg",

  dirtSrc +"26.jpg",

  dirtSrc +"27.jpg",

  dirtSrc +"28.jpg",

  dirtSrc +"29.jpg",

  dirtSrc +"30.jpg",

  dirtSrc +"31.jpg",

  dirtSrc +"32.jpg",

  dirtSrc +"33.jpg",

  dirtSrc +"34.jpg",

  dirtSrc +"35.jpg",

  dirtSrc +"36.jpg",

  dirtSrc +"37.jpg",

  dirtSrc +"38.jpg",

  dirtSrc +"39.jpg",

  dirtSrc +"40.jpg",

  dirtSrc +"41.jpg",

  dirtSrc +"42.jpg",

  dirtSrc +"43.jpg",

  dirtSrc +"44.jpg",

  dirtSrc +"45.jpg",

  dirtSrc +"46.jpg",

  dirtSrc +"47.jpg",

  dirtSrc +"48.jpg",

  dirtSrc +"49.jpg",

]};

//加载次数计数器

varscrollIndex = 0;

$(function(){

  /*监听窗口滚动情况*/

  $(window).on('scroll',function(){

    scrollTop = $(window).scrollTop();//$(window).scrollTop()==document.body.scrollTop

    clientHeight = $(window).height();

    scrollHeight = picList.last().height();//picList.last()[0].clientHeight

    /*目标与窗口的距离达到阈值时开始加载*/

    if(scrollHeight-clientHeight-scrollTop < threshold){

      scrollPic(10);

    }

  })

})

/*根据滚动程度加载图片，每次加载perAmount张*/

functionscrollPic(perAmount = 10){

  vartotalAmount = perAmount * (scrollIndex+1);

   //考虑到最后一次加载的时候，剩余的图片数量有可能达不到限定的每次加载的数量，这时候需要更改totalAmount的值

  if(totalAmount>picData.imgSrc.length){

    totalAmount = picData.imgSrc.length;

  }

  for(scrollIndex;scrollIndex

    varoimg =newImage();

    oimg.src = picData.imgSrc[scrollIndex];

    picList.append(oimg);

  }

}