由于js是单线程的加载，所以可以用alert执行顺序测试，执行结果为：
1→demo→2→3→5→4
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>jquery的加载测试</title>
<script src="http://libs.baidu.com/jquery/2.0.0/jquery.min.js"></script>
</head>
<body>
<style type="text/css">
.test{
width: 100px;
height: 100px;
margin: 10px;
border: 1px solid;
}
</style>
<script type="text/javascript">
alert(1)
$(function(){
alert(5)
})
</script>
<div id="d1" class="test"></div>
<div id="d2" class="test"></div>
<div id="d3" class="test"></div>
<div id="d4" class="test"></div>
<script type="text/javascript">
alert(2);
$(function(){
alert(4)
})
</script>
</body>
<script type="text/javascript">
alert(3)
</script>
</html>