Javascript 如何解决；未捕获类型错误：无法读取属性'；价值'；“无效”的定义；

我在ASP.NET中制作了我的第一份注册表格，并且使用了一些Javascript我在注册时出现了以下错误

未捕获的TypeError:无法读取null的属性“值”

以下是我的javascript代码：

function f_submitForm() {
    $("#submit").css("display", "none");
    $("#load").css("display", "block");


    const auxPriorityInput = document.getElementById("ticketPriorityInput");
    const auxticketService = document.getElementById("ticketServiceInput");
    const auxticketSubService = document.getElementById("ticketSubServiceInput");
    const auxCategoryInput = document.getElementById("ticketCategoryInput");
    const auxticketOrigin = document.getElementById("ticketOriginInput");

    const form = new FormData();

    const ins = document.getElementById("file").files.length;
    for (let x = 0; x < ins; x++) {
        form.append("files[]", document.getElementById("file").files[x]);
    }

    form.append("ticketIdAppliInput", document.getElementById("ticketIdAppliInput").value);
    form.append("ticketNameAppliInput", document.getElementById("ticketNameAppliInput").value);
    form.append("ticketEmailAppliInput", document.getElementById("ticketEmailAppliInput").value);    
    form.append("ticketExtAppliInput", document.getElementById("ticketExtAppliInput").value);
    form.append("ticketPhoneAppliInput", document.getElementById("ticketPhoneAppliInput").value);
    form.append("ticketAreaAppliInput", document.getElementById("ticketAreaAppliInput").value);
    form.append("ticketLocationAppliInput", document.getElementById("ticketLocationAppliInput").value);
    form.append("ticketSubjectInput", document.getElementById("ticketSubjectInput").value);
    form.append("ticketDescrInput", document.getElementById("ticketDescrInput").value);
    form.append("ticketPriorityInput", auxPriorityInput.options[auxPriorityInput.selectedIndex].value);
    form.append("ticketServiceInput", auxticketService.options[auxticketService.selectedIndex].value);
    form.append("ticketSubServiceInput", auxticketSubService.options[auxticketSubService.selectedIndex].value);
    form.append("ticketCategoryInput", auxCategoryInput.options[auxCategoryInput.selectedIndex].value);
    form.append("ticketOriginInput", auxticketOrigin.options[auxticketOrigin.selectedIndex].value);

扩展：

首先，请发布您的HTML。没有它，很难说发生了什么

---

但错误是相当直接的。在HTML中似乎没有包含

id=“ticketExtAppliInput”

的元素。检查拼写是否有误或为什么会丢失。这是

getElementById

返回

null

的最可能原因，该错误表明javascript找不到id为“ticketTextAppliInput”的元素。第一步是检查HTML并确保该元素的id拼写正确

---

更普遍的问题是，您在DOM中搜索元素，然后尝试访问它们的“value”属性。最佳做法是，在假设您可以获得该元素的值之前，确保您确实找到了该元素。

在反复研究之后，我找到了验证问题的解决方案，并按照以下方式进行了验证，如果该元素为空，请尝试进行验证。请分配值0

function f_submitForm() {
$("#submit").css("display", "none");
$("#load").css("display", "block");

const auxPriorityInput = document.getElementById("ticketPriorityInput");
const auxticketService = document.getElementById("ticketServiceInput");
const auxticketSubService = document.getElementById("ticketSubServiceInput");
const auxCategoryInput = document.getElementById("ticketCategoryInput");
const auxticketOrigin = document.getElementById("ticketOriginInput");


const form = new FormData();

const ins = document.getElementById("file").files.length;
for (let x = 0; x < ins; x++) {
    form.append("files[]", document.getElementById("file").files[x]);
}

form.append("ticketIdAppliInput", document.getElementById("ticketIdAppliInput").value);
form.append("ticketNameAppliInput", document.getElementById("ticketNameAppliInput").value);
form.append("ticketEmailAppliInput", document.getElementById("ticketEmailAppliInput").value);    
if ($('ticketExtAppliInput').val() == "") {

    //we give it the value of zero by not having any value
    document.getElementById("ticketExtAppliInput").value = "0";
} 
form.append("ticketPhoneAppliInput", document.getElementById("ticketPhoneAppliInput").value);
form.append("ticketAreaAppliInput", document.getElementById("ticketAreaAppliInput").value);
form.append("ticketLocationAppliInput", document.getElementById("ticketLocationAppliInput").value);
form.append("ticketSubjectInput", document.getElementById("ticketSubjectInput").value);
form.append("ticketDescrInput", document.getElementById("ticketDescrInput").value);
form.append("ticketPriorityInput", auxPriorityInput.options[auxPriorityInput.selectedIndex].value);
form.append("ticketServiceInput", auxticketService.options[auxticketService.selectedIndex].value);
form.append("ticketSubServiceInput", auxticketSubService.options[auxticketSubService.selectedIndex].value);
form.append("ticketCategoryInput", auxCategoryInput.options[auxCategoryInput.selectedIndex].value);
form.append("ticketOriginInput", auxticketOrigin.options[auxticketOrigin.selectedIndex].value);

函数f_submitForm（）{ $（“#提交”）.css（“显示”、“无”）； $（“#加载”）.css（“显示”、“块”）； const auxPriorityInput=document.getElementById（“ticketprioritynput”）； const auxticketService=document.getElementById（“ticketServiceInput”）； const auxticketSubService=document.getElementById（“ticketSubServiceInput”）； const auxCategoryInput=document.getElementById（“ticketCategoryInput”）； const auxticketOrigin=document.getElementById（“ticketOriginInput”）； const form=new FormData（）； const ins=document.getElementById（“文件”）.files.length； for（设x=0；x无法获取函数参数的

值

属性。以下是可从中获取值的快速列表。请检查HTML元素

“ticketTextAppliInput”

existsCheck在运行时检查浏览器开发工具。是否可能在调用之前删除、隐藏或重命名了此元素？浏览器说它不存在