我有一个带有HTML表单且内部带有文本字段的脚本，现在此文本字段仅允许数字。
尽管我希望文本字段仅允许数字，并且只允许变量+1的当前值。例如，假设变量的当前值（currentValue）为1，那么您可以在文本字段中输入的唯一数字是2。
这是我到目前为止的代码：
HTML：
<form id="value-form" action="value.php" method="POST" name="value-form">
<input onkeypress="return isNumberKey(event)" type="text" name="amount" id="amount" /> <!-- This is the text field I would like to only allow the value+1 -->
<input type="image" src="Button1.png" id="customButton" value="submit" alt="but"/>
</form>
Javascript：
function isNumberKey(evt) //This is the function I use to only allow numbers in the text field
{
var charCode = (evt.which) ? evt.which : event.keyCode
if (charCode > 31 && (charCode < 48 || charCode > 57))
return false;
return true;
}
var request = new XMLHttpRequest();
request.open('GET', 'currentValueFile.txt', false);
request.send();
var currentValue = request.responseText //this is the variable value I want to only allow +1 in the text field
document.getElementById("currentValue").innerHTML = currentValue;
<form id="value-form" action="value.php" method="POST" name="value-form">
<input onkeypress="return isNumberKey(event)" type="text" name="amount" id="amount" /> <!-- This is the text field I would like to only allow the value+1 -->
<input type="image" src="Button1.png" id="customButton" value="submit" alt="but"/>
</form>
<script type="text/javascript">
function toDec(code) {
return code - 48;
}
function isNumberKey(evt) //This is the function I use to only allow numbers in the text field
{
var charCode = (evt.which) ? evt.which : event.keyCode
if (charCode > 31 && (charCode < 48 || charCode > 57 || toDec(charCode) != currentValue + 1))
return false;
return true;
}
</script>
<script type="text/javascript">
var request = new XMLHttpRequest();
request.open('GET', 'currentValueFile.txt', false);
request.send();
var currentValue = parseInt(request.responseText) //this is the variable value I want to only allow +1 in the text field
</script>
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我来说两句