window.onload!= <body onload ="">

Question

window.onload!= <body onload ="">

And*_*nic 2 javascript collections onload

我认为这很有趣.考虑以下代码,window.onload和body onload =""都调用相同的函数.但是,结果不同.在我看来,window.onload存在集合问题.这是代码:

<html>
<script type="text/javascript">

    window.onload = getSpanElements();

    function getSpanElements(){
        var collectionBoolean = document.getElementsByTagName("span")?true:false;
        alert(
            "collection exists? " + collectionBoolean + "; number of collection members: " + document.getElementsByTagName("span").length
        );
    }


</script>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
    <title>Untitled Document</title>
</head>
<body onload="getSpanElements()">
    <span> test </span>
</body>

Run Code Online (Sandbox Code Playgroud)

如您所见,两者都报告集合存在,但window.onload报告它没有成员.有任何想法吗？