backend/app.js

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

//优先读取环境变量
require("dotenv").config()

//引入数据库连接
require("./dao/db")

//引入路由
const userRouter = require('./routes/user');
const expressRouter = require("./routes/express")

var app = express();

//配置cors
const corsOptions = {
  allowedHeaders: ['Content-Type', 'Authorization'],
  exposedHeaders: ['Authentication', 'X-Custom-Header'],
  credentials: true,
}
//为所有源跨域
app.use(cors(corsOptions))
//使用各种中间件
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')));

//使用路由中间件
app.use('/user', userRouter);
app.use("/express", expressRouter)

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

// 错误捕获
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);

});

module.exports = app;