JavaScript，匿名与直接函数调用

Question

In the following snippet I am assigning anonymous function to onreadystatechange variable and everything works fine, but if I assign a named function to this variable it does not work.

 <script language="Javascript">
    function postRequest(strURL) 
    {
        var xmlHttp;
        if (window.XMLHttpRequest) // Mozilla, Safari, ...
            var xmlHttp = new XMLHttpRequest();
        else if (window.ActiveXObject) // IE
            var xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
        xmlHttp.open('POST', strURL, true);
        xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        xmlHttp.onreadystatechange = function() 
        {
            alert("you are in anonymous");
        }
        xmlHttp.send(strURL);
    }
</script>

The above code works but the following does not. The function foo() does not get called:

 <script language="Javascript">
    function foo()
    {
        alert("you are in foo");
    }
    /*----------------------------------------------*/
    function postRequest(strURL) 
    {
        var xmlHttp;
        if (window.XMLHttpRequest) // Mozilla, Safari, ...
            var xmlHttp = new XMLHttpRequest();
        else if (window.ActiveXObject) // IE
            var xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
        xmlHttp.open('POST', strURL, true);
        xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        xmlHttp.onreadystatechange = foo; 
        xmlHttp.send(strURL);
    }
</script>

Why is that?

Answer 1

The issue was resolved. var xmlHttp had to be global. Although I am not using xmlHttp in foo(), maybe it is needed internally by xmlHttp object! Anybody knows why? Anyway this issue is resolved for me. Thanks