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<!DOCTYPE html>
<html>
<head>
<script src="//code.jquery.com/jquery-1.9.1.min.js"></script>
  <meta charset="utf-8">
  <title>JS Bin</title>
  <style>
    .container {
      max-width: 800px;
      margin: 0 auto;
    }
    .container:after{
      content: '';
      display: block;
      clear: both;
    }
    .container img {
      float: left;
      width: 50%;
    }
    h1{
      clear: both;
    }
  </style>
</head>
<body>
  <div class="container">
    <img src="http://smashinghub.com/wp-content/uploads/2014/08/cool-loading-animated-gif-3.gif" alt="1" data-src="http://cdn.jirengu.com/book.jirengu.com/img/1.jpg">
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    <img src="http://smashinghub.com/wp-content/uploads/2014/08/cool-loading-animated-gif-3.gif" alt="10" data-src="http://cdn.jirengu.com/book.jirengu.com/img/10.jpg">
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    <img src="http://smashinghub.com/wp-content/uploads/2014/08/cool-loading-animated-gif-3.gif" alt="14" data-src="http://cdn.jirengu.com/book.jirengu.com/img/14.jpg">
    <h1 id="target">hello</h1>
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    <img src="http://smashinghub.com/wp-content/uploads/2014/08/cool-loading-animated-gif-3.gif" alt="17" data-src="http://cdn.jirengu.com/book.jirengu.com/img/17.jpg">
    <img src="http://smashinghub.com/wp-content/uploads/2014/08/cool-loading-animated-gif-3.gif" alt="18" data-src="http://cdn.jirengu.com/book.jirengu.com/img/18.jpg">
    <img src="http://smashinghub.com/wp-content/uploads/2014/08/cool-loading-animated-gif-3.gif" alt="19" data-src="http://cdn.jirengu.com/book.jirengu.com/img/19.jpg">
    <img src="http://smashinghub.com/wp-content/uploads/2014/08/cool-loading-animated-gif-3.gif" alt="20" data-src="http://cdn.jirengu.com/book.jirengu.com/img/20.jpg">


  </div>
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    start()

    $(window).on('scroll', function(){
      start()
    })

    function start(){
      $('.container img').not('[data-isLoaded]').each(function(){
        var $node = $(this)
        if( isShow($node) ){
          loadImg($node)
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    function isShow($node){
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    function loadImg($img){
      $img.attr('src', $img.attr('data-src'))
      $img.attr('data-isLoaded', 1)
    }










  </script>
</body>
</html>

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