js获取所有被选中的checkbox值

    <label for=""><span>1</span><input type="checkbox" value="1"></label>    <label for=""><span>2</span><input type="checkbox" value="2"></label>    <label for=""><span>3</span><input type="checkbox" value="3"></label>    <label for=""><span>4</span><input type="checkbox" value="4"></label>    <button>提交</button>

    <script>        var oBtn = document.getElementsByTagName("button")[0];        oBtn.onclick = function(){            var oTxt = document.getElementsByTagName("input");            for (var i = 0; i < oTxt.length; i++) {                if(oTxt[i].checked){                    alert(oTxt[i].value);                }            }        }    </script>