要点

主要是app.use的callback中参数不同产生的多态，有err参数会处理错误，没有的会处理其他

code

//node
const express = require('express');
const fs = require('fs');
const path = require('path');
const app = express();
app.get('/', (req, res, next) => {
  try {
    const data = JSON.parse('{name:}');
    res.json(data);
  } catch (e) {
    next(e);
  }
});
app.get('/a', (req, res, next) => {
  res.end('<h1>Hello World!</h1>');
});
/*
* 处理404错误
* */
app.use((req,res,next)=>{
  res.writeHead(404,{'Content-Type':'text/html;charset=utf-8'});
  console.log('404');
  res.end('你访问的资源不存在');
});
/*
* 🙆统一的错误处理日志
* */
app.use((err, req, res, next) => {
  const error_log = `
    ======================
    错误名：${err.name},\n
    错误信息：${err.message},\n
    错误时间：${new Date()},\n
    错误堆栈：${err.stack},\n
    ======================
  `;
  fs.appendFile(path.join(__dirname, 'error.log'), error_log, err1 => {
    res.writeHead(500,{'Content-Type':'text/html;charset=utf-8'});
    res.end('500 服务器内部错误');
  })
});
app.listen(3000, () => {
  console.log('running......');
});