SOURCE

$('.bz').each(function(i,n){
    var obj = $(n);
    var val = obj.text();
    if(val == '' || val == null || val == undefined){
        alert(val);
        // wglx += "null,";
    }else{
        // wglx += obj.text() + ",";
        alert(val);
    }
});

<table>
        <tr>
            <td class="bz">  </td>
            <td class="bz"> 表的的值 </td>
        </tr>
    </table>