在表单发布请求期间未定义变量答案

【问题标题】：variable is not defined during the form post request在表单发布请求期间未定义变量
【发布时间】：2021-05-23 02:14:39
【问题描述】：

我需要通过 html 表单发送值并在 console.log 中接收它。但是一旦我发送数据，即使我在表单名称中声明了它，也会弹出错误“TypeError：无法读取未定义的属性'fName'”。

signin.html：

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <meta name="description" content="">
    <meta name="author" content="Mark Otto, Jacob Thornton, and Bootstrap contributors">
    <meta name="generator" content="Hugo 0.80.0">
    <title>Signin Template · Bootstrap v5.0</title>

    <link rel="canonical" href="https://getbootstrap.com/docs/5.0/examples/sign-in/">



    <!-- Bootstrap core CSS -->
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">


    <!-- Favicons -->
<link rel="apple-touch-icon" href="/docs/5.0/assets/img/favicons/apple-touch-icon.png" sizes="180x180">
<link rel="icon" href="/docs/5.0/assets/img/favicons/favicon-32x32.png" sizes="32x32" type="image/png">
<link rel="icon" href="/docs/5.0/assets/img/favicons/favicon-16x16.png" sizes="16x16" type="image/png">
<link rel="manifest" href="/docs/5.0/assets/img/favicons/manifest.json">
<link rel="mask-icon" href="/docs/5.0/assets/img/favicons/safari-pinned-tab.svg" color="#7952b3">
<link rel="icon" href="/docs/5.0/assets/img/favicons/favicon.ico">
<meta name="theme-color" content="#7952b3">


    <style>
      .bd-placeholder-img {
        font-size: 1.125rem;
        text-anchor: middle;
        -webkit-user-select: none;
        -moz-user-select: none;
        user-select: none;
      }

      @media (min-width: 768px) {
        .bd-placeholder-img-lg {
          font-size: 3.5rem;
        }
      }
    </style>


    <!-- Custom styles for this template -->
    <link href="css/styles.css" rel="stylesheet">
  </head>
  <body class="text-center">

<main class="form-signin">
  <form action="/" method="POST">

    <img class="mb-4" src="images/logo.jpg" alt="" width="72" height="57">
    <h1 class="h3 mb-3 fw-normal">Sign Up Here</h1>
    <input type="text" name ="fName" class="form-control top" placeholder="First Name" required autofocus>
    <input type="text" name ="lName" class="form-control middle" placeholder="Last Name" required>
    <input type="email" name ="email" class="form-control bottom" placeholder="Email" required>

    <button class="w-100 btn btn-lg btn-primary signinbutton" type="submit">Sign Up!</button>
    <p class="mt-5 mb-3 text-muted">&copy; The ThunderStorm</p>
  </form>
</main>



  </body>
</html>

app.js：

//jshint esversion:6

const express = require('express');
const bodyParser = require('body-parser');
const request = require('request');

const app = express();
app.use(express.static("public"));
app.use(bodyParser.urlencoded({extended: true}));

app.get('/', function(req, res){

  res.sendFile(__dirname + "/signup.html");
});

app.post("/",function(req,res){

  var firstName = res.body.fName;
  var lastName = res.body.lName;
  var email = res.body.email;

  console.log(firstName,lastName,email);
});




app.listen(3000,function(){
  console.log("Started listening on port 3000");
});

错误日志：

TypeError：无法读取未定义的属性“fName” 在 G:\WebDevelopmentFolder\Newsletter-Signup\app.js:18:28 在 Layer.handle [as handle_request] (G:\WebDevelopmentFolder\Newsletter-Signup\node_modules\express\lib\router\layer.js:95:5) 在下一个 (G:\WebDevelopmentFolder\Newsletter-Signup\node_modules\express\lib\router\route.js:137:13) 在 Route.dispatch (G:\WebDevelopmentFolder\Newsletter-Signup\node_modules\express\lib\router\route.js:112:3) 在 Layer.handle [as handle_request] (G:\WebDevelopmentFolder\Newsletter-Signup\node_modules\express\lib\router\layer.js:95:5) 在 G:\WebDevelopmentFolder\Newsletter-Signup\node_modules\express\lib\router\index.js:281:22 在 Function.process_params (G:\WebDevelopmentFolder\Newsletter-Signup\node_modules\express\lib\router\index.js:335:12) 在下一个 (G:\WebDevelopmentFolder\Newsletter-Signup\node_modules\express\lib\router\index.js:275:10) 在 G:\WebDevelopmentFolder\Newsletter-Signup\node_modules\body-parser\lib\read.js:130:5 在 invokeCallback (G:\WebDevelopmentFolder\Newsletter-Signup\node_modules\raw-body\index.js:224:16)

【问题讨论】：

错误信息是“Cannot read property 'fName' of undefined”，而不是“'fName' is 未定义”。 res.body 是 undefined。

标签： javascript node.js express

【解决方案1】：

您需要从request 对象中读取正文。

const firstName = req.body.fName;
const lastName = req.body.lName;
const email = req.body.email;

【讨论】：