不能判断正误，输入不同东西出现一样的东西

html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Documenttitle>
head>

<body>
    <form id="form1" name="form1" method="post" action="">
        <fieldset>
            <legend>根据出生年份计算生肖legend>
            <p align="center">请输入<span style="color:red ;font-weight: 600;">2122班span>的出生年份：
                <input name="txtYear" type="text" id="txtYear" size="12" />
                <input name="btnShow" type="button" id="btnShow" value="显示生肖" onclick="showShengxiao();" />
            p>
            <p id="Shengxiao" align="center"> p>
        fieldset>

    form>
    <script>
        var year = Number(document.getElementById("txtYear").innerHTML);

        function showShengxiao() {
            if (isNaN(year)) {
                alert("请输入正确年份");
            } else {
                switch (year % 12) {
                    case 0:
                        document.getElementById("Shengxiao").innerHTML = "猴";
                        break;
                    case 1:
                        document.getElementById("Shengxiao").innerHTML = "鸡";
                        break;
                    case 2:
                        document.getElementById("Shengxiao").innerHTML = "狗";
                        break;
                    case 3:
                        document.getElementById("Shengxiao").innerHTML = "猪";
                        break;
                    case 4:
                        document.getElementById("Shengxiao").innerHTML = "鼠";
                        break;
                    case 5:
                        document.getElementById("Shengxiao").innerHTML = "牛";
                        break;
                    case 6:
                        document.getElementById("Shengxiao").innerHTML = "虎";
                        break;
                    case 7:
                        document.getElementById("Shengxiao").innerHTML = "兔";
                        break;
                    case 8:
                        document.getElementById("Shengxiao").innerHTML = "龙";
                        break;
                    case 9:
                        document.getElementById("Shengxiao").innerHTML = "蛇";
                        break;
                    case 10:
                        document.getElementById("Shengxiao").innerHTML = "马";
                        break;
                    case 11:
                        document.getElementById("Shengxiao").innerHTML = "羊";
                        break;
                }
            }
        }
    script>
body>

html>

请问为什么我每次输入不同的数字，出来的是同一个·生肖，而且系统也不会判断是否正确

你获取 input的值需要用value属性而且你这个方法有些不对。似乎属相有问题不过给你解决了不变的问题


<!DOCTYPE html>
<html lang="en">
 
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
 
<body>
    <form id="form1" name="form1" method="post" action="">
        <fieldset>
            <legend>根据出生年份计算生肖</legend>
            <p align="center">请输入<span style="color:red ;font-weight: 600;">2122班</span>的出生年份：
                <input name="txtYear" type="text" id="txtYear" size="12" />
                <input name="btnShow" type="button" id="btnShow" value="显示生肖" onclick="showShengxiao()" />
            </p>
            <p id="Shengxiao" align="center"> </p>
        </fieldset>
 
    </form>
    <script>
        var year = document.getElementById("txtYear");
      
        function showShengxiao() {
            console.log(year.value)
            if (isNaN(Number(year.value))) {
                alert("请输入正确年份");
            } else {
                switch (year.value % 12) {
                    case 0:
                        document.getElementById("Shengxiao").innerHTML = "猴";
                        break;
                    case 1:
                        document.getElementById("Shengxiao").innerHTML = "鸡";
                        break;
                    case 2:
                        document.getElementById("Shengxiao").innerHTML = "狗";
                        break;
                    case 3:
                        document.getElementById("Shengxiao").innerHTML = "猪";
                        break;
                    case 4:
                        document.getElementById("Shengxiao").innerHTML = "鼠";
                        break;
                    case 5:
                        document.getElementById("Shengxiao").innerHTML = "牛";
                        break;
                    case 6:
                        document.getElementById("Shengxiao").innerHTML = "虎";
                        break;
                    case 7:
                        document.getElementById("Shengxiao").innerHTML = "兔";
                        break;
                    case 8:
                        document.getElementById("Shengxiao").innerHTML = "龙";
                        break;
                    case 9:
                        document.getElementById("Shengxiao").innerHTML = "蛇";
                        break;
                    case 10:
                        document.getElementById("Shengxiao").innerHTML = "马";
                        break;
                    case 11:
                        document.getElementById("Shengxiao").innerHTML = "羊";
                        break;
                }
            }
        }
    </script>
</body>
 
</html>

year获取值放入showShengxiao中