Jquery Ajax IE8 看過來?。?！

ie8下ajax的headers里的token值取不到，什么原因??？急急急~~~

<input type="button" value=123" onclick="up();"/>
<script type="text/javascript">
    function up(){
        var jsonData = {
            customerno:'1011596229328502786'
        }
        var str = JSON.stringify(jsonData)
        jQuery.support.cors = true; 
        $.ajax({
            type:'post',
            url:Router+'eccustomer/isNullPolicy',
            data:str,
            contentType:'application/json;charset=UTF-8',
            async: true,
            dataType:'json', 
            headers:{
                token: '123'
            },
            success:function(res){  
                
            },
            error:function(err){
                alert('error')
            }
        })
    }
</script>