express初始化项目完成后启动项目打开浏览器显示NotFound？

Question

用express初始化项目以后，什么都没改先启动一下项目npm start
打开浏览器localhost:3000能正常访问并显示

然后学着连接数据库读取数据。
用node命令运行了一下程序，连接并读取了数据。

想在浏览器里看看效果，但是再启动就报NotFound？

app.js的代码(这里代码都没动)

var createError = require('http-errors');
var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');

var indexRouter = require('./routes/index');
var usersRouter = require('./routes/users');

var app = express();

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/', indexRouter);
app.use('/index',indexRouter);
app.use('/users', usersRouter);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  next(createError(404));
});

// error handler
app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.render('error');
});

module.exports = app;

serverroutesindex.js的代码

var express = require('express');
var router = express.Router();

const conn = require('../db');

conn.query('select * from city where id=1',function(err,rows,fields){
  if(err){
    console.log('[query]-'+err);
    return;
  }else{
    console.log("连接成功");
  }  
  console.log(rows[0]);
  //console.log(fields);
})
//关闭connection
conn.end(function(err){
  if(err)
    return;
  console.log('[connection end] succeed!');
})

/* GET home page. */
router.get('/', function(req, res, next) {
  res.send('respond with a resource');
});

module.exports = router;

db.js的代码(db.js跟app.js在同一目录下)

const mysql=require('mysql');

const conn=mysql.createConnection({
    host:'127.0.0.1',
    user:'root',
    password:'123456',
    database:'world',
    multipleStatements:true
});

conn.connect();

module.exports=conn;

并且访问users没问题！
localhost:3000/users

为什么访问index找不到？

Answer 1

NotFound就是没有没有找到对应的url，或者url对应的路由没有返回内容，你看看/index，有对应的路由处理吗？