如何使用 Javascript 在 HTML 文本框上设置最小和最大字符长度
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How to set a min and max character length on a HTML textbox using Javascript
提问by user1990084
I am only GCSE level and I need a text box in my code to only have 4 characters. I have made it a max of 4 but I need it to have a minimum of 4 aswell. I also made it only accept numbers. I am not using HTML 5 at my school.
我只有 GCSE 水平，我的代码中需要一个文本框，只有 4 个字符。我已将它设置为最多 4 个，但我还需要它至少为 4 个。我也让它只接受数字。我在学校没有使用 HTML 5。
This is my whole code:
这是我的全部代码：
<head>
<title>Exam entry</title>
<script language="javascript" type="text/javascript">
function validateForm() {
var result = true;
var msg="";
if (document.ExamEntry.name.value=="") {
msg+="You must enter your name \n";
document.ExamEntry.name.focus();
document.getElementById('name').style.color="red";
result = false;
}
if (document.ExamEntry.subject.value=="") {
msg+="You must enter the subject. \n";
document.ExamEntry.subject.focus();
document.getElementById('subject').style.color="red";
result = false;
}
if (document.ExamEntry.ExamNumber.value=="") {
msg+="You must enter your exam number. \n";
document.ExamEntry.ExamNumber.focus();
document.getElementById('ExamNumber').style.color="red";
result = false;
}
if(document.ExamEntry.ExamNoLen.value.length <4) {
msg+="Your eaxm nuber must be 4 digits long. \n";
document.ExamEntry.ExamNumber.focus();
document.getElementById('ExamNumber').style.color="red";
result = false;
}
checkInput(elem){
if(elem.value.length != 4){
alert("This value needs to be 4 characters long!");
elem.value = ""; // Reset the textbox
}
else{
alert("This value is 4 characters long.");
}
}
if(msg==""){
return result;
}
{
alert(msg)
return result;
}
}
</script>
</head>
<body>
<h1>Exam Entry Form</h1>
<form name="ExamEntry" method="post" action="success.html">
<table width="50%" border="0">
<tr>
<td id="name">Name</td>
<td><input type="text" name="name" /></td>
</tr>
<tr>
<td id="subject">Subject</td>
<td><input type="text" name="subject" /></td>
</tr>
<tr>
<td id="ExamNumber">Exam Number </td>
<td>
<input name="ExamNumber" type="text"
onkeydown="return ( event.ctrlKey || event.altKey
|| (47<event.keyCode && event.keyCode<58 && event.shiftKey==false)
|| (95<event.keyCode && event.keyCode<106)
|| (event.keyCode==8) || (event.keyCode==9)
|| (event.keyCode>34 && event.keyCode<40)
|| (event.keyCode==46) )"
maxlength="4" onblur="checkInput(this)" />
</td>
</tr>
<tr>
<td><input type="submit" name="Submit" value="Submit" onClick="return validateForm();" /></td>
<td><input type="reset" name="Reset" value="Reset" /></td>
</tr>
</table>
</form>
</body>
回答by George
Well you can't have a minlength because your users are going to need to type 1,2 and 3 characters to get to 4. (Unless you apply some sort of input mask which is more advanced). But you can check that it is 4 characters long when it is blurred..
好吧，您不能有 minlength，因为您的用户将需要键入 1,2 和 3 个字符才能达到 4。（除非您应用某种更高级的输入掩码）。但是当它模糊时，您可以检查它是否为 4 个字符长。
<input name="ExamNumber" type="text" onblur="checkInput(this)" onkeydown="return ( event.ctrlKey || event.altKey || (47<event.keyCode && event.keyCode<58 && event.shiftKey==false) || (95<event.keyCode && event.keyCode<106) || (event.keyCode==8) || (event.keyCode==9) || (event.keyCode>34 && event.keyCode<40) || (event.keyCode==46) )" maxlength="4" />
And then a simple JavaScript function..
然后是一个简单的 JavaScript 函数..
function checkInput(elem){
if(elem.value.length != 4){
alert("This value needs to be 4 characters long!");
elem.value = ""; // Reset the textbox
}
else{
alert("This value is 4 characters long.");
}
}
