javascript

jQuery simply implements image preloading

jQuery implements image preloading

JS code

$(function(){
   loadImg("http://d.hiphotos.baidu.com/image/pic/item/fd039245d688d43f14f69eff7f1ed21b0ef43b5b.jpg",addImg);
  function loadImg(url,callback){
    var img = new Image();
    img.onload = function(){
      img.onload = null;
      callback(img);
    }
    img.src=url;
    img.width ="202";
    img.height = "202";
    img.attr("defaulturl","../images/img.png");
    if(){}
  }
  function addImg(img){
    $(img).appendTo($(".imgload li"))
  }
})

HTML:

<!doctype html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title> Image preloading </title>
  <link rel="stylesheet" type="text/css" href="css/index.css">
  <script type="text/javascript" src="js/jquery-1.8.3.min.js"></script>
  <script type="text/javascript" src="js/index.js"></script>
</head>
<body>

    <div class="imgload">
      <ul>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
      </ul>
    </div>
</body>
</html>

Other instances

function loadimg(arr,funLoading,funOnLoad,funOnError){
  var numLoaded=0,
  numError=0,
  isObject=Object.prototype.toString.call(arr)==="[object Object]" ? true : false;

  var arr=isObject ? arr.get() : arr;
  for(a in arr){
    var src=isObject ? $(arr[a]).attr("data-src") : arr[a];
    preload(src,arr[a]);
  }

  function preload(src,obj){
    var img=new Image();
    img.onload=function(){
      numLoaded++;
      funLoading && funLoading(numLoaded,arr.length,src,obj);
      funOnLoad && numLoaded==arr.length && funOnLoad(numError);
    };
    img.onerror=function(){
      numLoaded++;
      numError++;
      funOnError && funOnError(numLoaded,arr.length,src,obj);
    }
    img.src=src;
  }

}

Parameter description: arr: can be an array to store the image path, or the jquery object selected from img; funLoading: the operation performed after each individual picture is loaded; funOnLoad: the operation after all the pictures are loaded; funOnError: operation when a single image is loaded incorrectly.

Lazy loading,

var imgonload=function(errors){
    /*errors : the number of images loaded incorrectly; */
  console.log("loaded,"+errors+" images loaded error!");
}

var funloading=function(n,total,src,obj){
    /*
    n : the number of completed loads;
    total : the total number of images to be loaded;
    src : the image path that has been loaded;
    obj : when loadimg Passed in from the function arr When storing an array of image paths, obj=src , is the image path,
         when arr for jquery Object, obj Is the current load completed img dom Object.
    */
  console.log(n+"of"+total+" pic loaded.",src);
  var newimg = document.createElement("img");
  newimg.src=src;
  $("body").append(newimg).fadeIn();
}

var funloading_obj=function(n,total,src,obj){
  console.log(n+"of"+total+" pic loaded.",src);
  $(obj).attr("src",src);
  $(obj).fadeIn(200);
}

var funOnError=function(n,total,src,obj){
  console.log("the "+n+"st img loaded Error!");
}

Debugging use cases

console.log("loading...");
loadimg($("img"),funloading_obj,imgonload,funOnError);
/*loadimg(["http://pic22.nipic.com/20120619/9607634_212642465144_2.jpg",
     "http://pic21.nipic.com/20120531/1670912_103610084349_2.jpg",
     "http://pic21.nipic.com/20120616/4952071_130629530136_2.jpg",
     "http://pic21.nipic.com/20120610/1723580_105037029000_2.jpg",
     "http://pic22.nipic.com/20120617/2572038_125013326121_2.jpg"
    ],funloading,imgonload,funOnError);*/

That’s all for this article, I hope you enjoy it.