Javascript如何获取选中checkbox的值

<input type="checkbox" name="test" value="1"/><span>1</span>
<input type="checkbox" name="test" value="2"/><span>2</span>
<input type="checkbox" name="test" value="3"/><span>3</span>
<input type='button' value='提交' onclick="fun()"/>

function fun(){
obj = document.getElementsByName("test");
check_val = [];
for(k in obj){
if(obj[k].checked)
check_val.push(obj[k].value);
}
alert(check_val);
}