checkbox 和 radio 单选和复选，js取值

<script>
function check(){
var sjbz = '';
    var blackName = document.getElementsByName("sj");
    for(var i = 0; i < blackName.length; i++)
    {

    if(blackName[i].checked == true)
       {
         sjbz= blackName[i].value;
       }
       }

    alert(sjbz);
    }
    </script>
 <input type="radio" name="sj" value ="1" >在册数据
<input type="radio" name="sj" value ="0" checked>历史数据

<input type="button" value="111" onclick="check()">

//以下为复选

<script>
function check(){
var sjbz1 = document.getElementById("sj1");
var sjbz2 = document.getElementById("sj2");
    alert(sjbz);
    }
    </script>
 <input type="checkbox" name="sj1" value ="1" >在册数据
<input type="checkbox" name="sj2" value ="0" checked>历史数据

<input type="button" value="111" onclick="check()">