今天我們來實作登入畫面，我會先預設一個登入畫面，可以輸入帳號密碼，輸入正確後會顯示登入成功，否則會跳轉至失敗，以下為程式碼:

const http = require("http");
const fs = require("fs");
const path = require("path");
const qs = require("querystring");

const port = 3000;
const ip = "127.0.0.1";

const sendResponse = (filename, statusCode, response) => {
  const filePath = path.join(__dirname, filename);
  fs.readFile(filePath, (error, data) => {
    if (error) {
      console.error(`Error reading file: ${filename}`);
      console.error(error);
      response.statusCode = 500;
      response.setHeader("Content-Type", "text/plain");
      response.end("Sorry, internal error");
    } else {
      response.statusCode = statusCode;
      response.setHeader("Content-Type", "text/html");
      response.end(data);
    }
  });
};

const server = http.createServer((request, response) => {
  const method = request.method;
  const url = request.url;

  if (method === "GET") {
    if (url === "/") {
      sendResponse("login.html", 200, response);
    } else if (url === "/success.html") {
      sendResponse("success.html", 200, response);
    } else if (url === "/fail.html") {
      sendResponse("fail.html", 200, response);
    } else {
      sendResponse("404.html", 404, response);
    }
  } else if (method === "POST" && url === "/process-login") {
    let body = "";

    request.on("data", (chunk) => {
      body += chunk.toString();
    });

    request.on("end", () => {
      const formData = qs.parse(body);

      if (formData.username.toLowerCase() === "aaa" && formData.password === "123456") {
        response.writeHead(302, {
          Location: "/success.html"
        });
        response.end();
      } else {
        response.writeHead(302, {
          Location: "/fail.html"
        });
        response.end();
      }
    });
  } else {
    sendResponse("404.html", 404, response);
  }
});

server.listen(port, ip, () => {
  console.log(`Server is running at http://${ip}:${port}`);
});

這是node.js的主要程式碼，其餘html的三個文件就簡單地做分別，不過我的登入結果還有一點問題需要處理，我將修正它以及詳細講解。