JavaScript表單驗證沒有工作，不能魚翅爲什麼

Question

所以我有這個網站：

<form action="insert.php" method="post" onsubmit="return validateForm(this)"> 
<label for="FUP start date">FUP start date:</label> 
<input type="text" name="inputField" id="inputField"/> 
</br> 
</br> 
<label for="FUP end date">FUP end date:&nbsp;</label> 
<input type="text" name="inputField2" id="inputField2" /> 
</br> 
</br> 
<label for="Allowed traffic">Allowed traffic:</label> 
<input type="text" name="Allowed_traffic" id="Allowed_traffic"/> 
</br> 
</br> 
<label for="Frequency">Frequency:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</label> 
<input type="text" name="Frequency" id="Frequency" /> 
</br> 
</br> 
<input type="submit" value="submit"> 
</form> 

而且這個JavaScript密碼（帕羅拉）：

<script> 
function validateForm(formElement) { 
    if (formElement.Allowed_traffic.length < 5) { 
    alert('aaaPlease enter a password that is at least 5 characters long'); 
    return false; 
} 
if (formElement.Allowed_traffic.length > 10) { 
    alert('Please enter a password that is less than 10 characters long'); 
    return false; 
} 
} 

</script> 

我在做什麼錯？我想檢查一下提交的密碼是否在5到10個字符之間。 謝謝！

Answer 1

用.value.length代替.length。

Answer 2

您目前正在查看<input>元素本身的length屬性（可能不存在）。你想在看什麼<input>元素的值的length財產，所以做到以下幾點：

if (formElement.Allowed_traffic.value.length < 5) { 
    alert('aaaPlease enter a password that is at least 5 characters long'); 
    return false; 
} 
else if (formElement.Allowed_traffic.value.length > 10) { 
    alert('Please enter a password that is less than 10 characters long'); 
    return false; 
} 

請注意，我把它改成一個if ... else if因爲如果第一個條件爲真那麼第二個不能。

Answer 3

嘗試使用

var Allowed_traffic = document.getElementById("Allowed_traffic"); 

代替

formElement.Allowed_traffic