当我尝试使用猫鼬的“ findByIdAndRemove”方法时，为什么我的EJS变量返回“未定义”

我试图在单击按钮时从mongoDB数据库中删除记录。但是，当我在控制台上记录此按钮的值时，它将返回“未定义”

下面是ejs文件

<%- include("partials/header") -%>

<h1>Home</h1>

<!-- A variable for the homepage that is populated by a body of text passed from app.js -->
<p><%= homeText %> </p>

<a class= "btn btn-primary" href="/compose" role="button">Compose a new post</a>

<%# A forEach method with a function holding a parameter of "post" which represents an element in an array, then displaying the element's title and content. %>
<% homeContent.forEach(function(post){ %>
<h1><%= post.title %></h1>
<!-- Displays only the first 100 characters of a post as well as a "read more" hyperlink which directs to a "post" page containing the full content of the post. -->
<p><%= post.content.substring(0, 100) + " ... " %> <a href="/post/<%=post._id %>">Read more</a></p>

<form action = "/delete", method="Post">
  <button type="button" class ="btn btn-link" name = "deleteButton" value = "<%=post._id%>" onClick="this.form.submit()"  ><svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" class="bi bi-trash" viewBox="0 0 16 16">
  <path d="M5.5 5.5A.5.5 0 0 1 6 6v6a.5.5 0 0 1-1 0V6a.5.5 0 0 1 .5-.5zm2.5 0a.5.5 0 0 1 .5.5v6a.5.5 0 0 1-1 0V6a.5.5 0 0 1 .5-.5zm3 .5a.5.5 0 0 0-1 0v6a.5.5 0 0 0 1 0V6z"/>
  <path fill-rule="evenodd" d="M14.5 3a1 1 0 0 1-1 1H13v9a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2V4h-.5a1 1 0 0 1-1-1V2a1 1 0 0 1 1-1H6a1 1 0 0 1 1-1h2a1 1 0 0 1 1 1h3.5a1 1 0 0 1 1 1v1zM4.118 4L4 4.059V13a1 1 0 0 0 1 1h6a1 1 0 0 0 1-1V4.059L11.882 4H4.118zM2.5 3V2h11v1h-11z"/>
</svg> </button>   %>

  </form>


<%});%>



<%- include("partials/footer") -%>

这是我试图在我的app.js（服务器文件）中调用我的删除功能的方法

app.post("/delete", function(req,res){
  const selectedId = req.body.deleteButton;

  Post.findByIdAndRemove(selectedId, function(err){
    if(!err){
      console.log(selectedId);
      res.redirect("/");
    }
  })
});

当我在控制台上登录ID变量时，很明显它没有正确地从EJS文件访问帖子的ID，因为它返回“ undefined”，因此没有任何内容被删除。有什么明显的我想念的地方吗？我对MongoDB和NodeJS还是很陌生，我一直在寻找一些答案，但似乎无法确定我写的语法上有什么错误。如果您需要更多我的代码，请随时告诉我，谢谢！