判斷是否有選擇值：

 var count = 0;
    $("input[name=subBox]:checkbox:checked").each(function () {
        count++;
    })

獲取選擇的值： 

var contract = $("input[name=subBox]:checkbox:checked").val();

程式碼：

   頁面

<td class="table-check"><input name="subBox" type="checkbox" value="{{= contract}}" onclick='countNum(this);'></td>
 

  js 

function checkdownContract() {
    var count = 0;
    $("input[name=subBox]:checkbox:checked").each(function () {
        count++;
    })
    if (count == 0 || count > 1) {
        if (count == 0) {
            alert("請選擇");
        } else {
            alert("一次只能選擇一個下載");
        }
        return false;
    }
    //../../../loanQuery/downSingWithContract
    if (count == 1) {
        var contract = $("input[name=subBox]:checkbox:checked").val();
        window.location.href = "../../../loanQuery/downSingWithContract?contract=" + contract;
        return false;
    }
}