Javascript getElementById行为异常

这是:
seatNum-循环通过的座椅数量

当我尝试获取id命名约定为“s1”、“s2”和“s3”等的元素时,问题出现在for循环中s45“s46”等。。。基于添加到起始座椅的回路计数器。从0(起始座位)到seatNum(多少座位)计数。

知道为什么by id不能正确解析吗?除了for循环中的最后一个外,其他所有的都可以正常工作。

function check() {
    var startSeat;
    var fName = document.getElementById('fName').value
    var lName = document.getElementById('lName').value
    var address = document.getElementById('address').value
    var city = document.getElementById('city').value
    var state = document.getElementById('state').value
    var zip = document.getElementById('zip').value
    var phone = document.getElementById('phone').value
    var seatNum = document.getElementById('seatNumber').value
    var y=document.getElementById('seatList1').value;
    var z=document.getElementById('seatList2').value;

    if (z >= y) {
        startSeat = y;
    }
    else {
        startSeat = z;
    }

    if ( (fName == "") || (lName == "") || (address == "") || (phone == "") || (zip == "") || (state == "") || (city == "") ) {
        alert("You must fully complete the form");
        return false;
    }

    for (var i = 0; i < seatNum; i++) {
        if (document.getElementById("s"+(startSeat+i)).className=="taken"){
            alert("Selected seat(s) already booked.");
            return false;
        }
    else {
            continue;
        }
    }
}