Detect Input

java script 偵測文字方塊輸入剩多少字：https://www.itread01.com/article/1535775467.html

判斷剩多少字能輸入：https://www.itread01.com/article/1423012706.html

圖書館簽到系統

判斷輸入數字位數

<title></title> 

    <script type="text/javascript"> 

        var maxstrlen = 6; 

        function Q(s) { return document.getElementById(s); } 

        function checkWord6(c) { 

            len = maxstrlen; 

            var str = c.value; 

            myLen = getStrleng(str); 

            var wck = Q("wordCheck6"); 

  

            if (myLen > len) { 

                c.value = str.substring(0, i + 1); 

            } 

            else { 

                wck.innerHTML = "已經讀入" + Math.floor((myLen)) + "個數字。";

if (myLen == len){

wck.innerHTML = "[執行呼叫GAS]";

location.href = 'https://www.javascripttutorial.net/';

}

            } 

        } 

        function getStrleng(str) { 

            myLen = 0; 

            i = 0; 

            for (; (i < str.length) && (myLen <= maxstrlen * 2); i++) { 

                if (str.charCodeAt(i) > 0 && str.charCodeAt(i) < 128) 

                    myLen++; 

                else 

                    myLen += 2; 

            } 

            return myLen; 

        } 

     

    </script> 


</head>

<body>


<form id="form1" runat="server">


<Table width="100%" bgcolor="Yellow">

<Tr><TD align="center"><h1>國立岡山高中圖書館K書中心簽到系統</h1></TD></Tr>

<Tr><TD align="center">

  <table ="1" bordercolor="Green">

    <caption>讀卡感應區_JavaScript</caption>

    <tr>

      <td>簽到、退學號：<input type="text" onkeyup="javascript:checkWord6(this);" placeholder="感應學號" size="14" maxlength="6" autofocus /></td>

    </tr>

    <tr><td>

<ul>

    <li>請感應學生證讀取學號。</li>

    <li>收到系統通知信才是簽到成功。</li>

    <li>維護自身權益確實簽到。</li>

</ul>

    </td></tr>

    <tr><td><span style="font-family: Georgia; font-size: 26px;" id="wordCheck6">目前讀入0個字元。</span></td>

    </tr>

  </table>

</TD>

</Tr>


</Table>


</form>


</body>

</html>