使用node 实现文件修改，自动刷新浏览器功能 （HTTP 轮询

/**
 * # 使用node实现静态文件服务器，仿nginx 静态服务器
 */
let http = require("http")
let url = require("url")
let fs = require("fs")
let net = require('net')

let fileIsModify = false  // 文件是否修改
// 默认端口，并检测端口是否被占用
let port = 8100
portIsOccupied(port).then(() => {
  createServerFn();
})

function createServerFn() {
  http.createServer(function (req, res) {
    let reqPath = url.parse(req.url).path
    let filepath = __dirname + reqPath
    if (!reqPath.includes('.')) {
      if (reqPath == '/server/refresh') {
        if (fileIsModify) {
          res.end('{"code":"2000","success":true, "refresh":true}')
          fileIsModify = false
        } else {
          res.end('{"code":"2000","success":true, "refresh":false}')
        }
      }
      return
    }
    fs.exists(filepath, function (exists) {
      if (exists) {
        fs.stat(filepath, function (err, stats) {
          if (err) {
            res.end('<h1>server error</h1><p>' + err + '</p>')
          } else {
            if (stats.isFile()) {
              if (filepath.includes('html')) {
                dealHtmlFile(filepath, res)
                return
              }
            } else {
              fs.readdir(filepath, function (err, files) {
                if (files.includes('index.html')) {
                  filepath = filepath + 'index.html'
                  dealHtmlFile(filepath, res)
                } else {
                  res.end('<h1>404 no such file or directory</h1><p>no such file or directory</p><p>' + filepath + '/index.html</p>')
                }
              })
            }
          }
        })
      } else {
        res.end('<h1>404 no such file or directory</h1><p>no such file or directory</p><p>' + filepath + '</p>')
      }
    })
  }).listen(port)
  console.log('http.createServer is start, port ' + port)
}
// 检测端口是否被占用
function portIsOccupied() {
  const server = net.createServer().listen(port)
  return new Promise((resolve, reject) => {
    server.on('listening', () => {
      server.close()
      resolve()
    })
    server.on('error', (err) => {
      if (err.code === 'EADDRINUSE') {
        port++
        resolve(portIsOccupied())
      } else {
        reject(err)
      }
    })
  })
}
// 检测文件是否修改
fs.watch(__dirname,{recursive: true},function (event, filename) {
  fileIsModify = true
})
// html 文件特殊处理
function dealHtmlFile(filepath, res) {
  var data = fs.readFileSync(filepath, 'utf-8')
  let scriptStr = `
    <script>
      let origin = location.origin
      var xhr = new XMLHttpRequest();
      xhr.onload = function () {
        if (xhr.status === 200) {
          let respData = JSON.parse(xhr.response)
          console.log(respData)
          if (respData.refresh) {
            location.reload()
          }
        }
      }
      setInterval(function(){
        xhr.open('GET', origin + '/server/refresh', true);
        xhr.send(null);
      },1000)
    </script>
  `
  data += scriptStr
  res.end(data)
}