data_dashboards/server/app.js

 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');
require('./db/mysql')
var app = express();


// 配置跨域中间件
app.use((req, res, next) => {
  // 允许所有来源访问，生产环境应谨慎设置，可替换为具体域名
  res.setHeader('Access-Control-Allow-Origin', '*');
  // 允许的请求方法
  res.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
  // 允许的请求头
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');
  // 处理 OPTIONS 预检请求，直接返回 204 状态码
  if (req.method === 'OPTIONS') {
      res.sendStatus(204);
  } else {
      next();
  }
});

// view engine setup
// app.set('views', path.join(__dirname, 'views'));
// app.set('view engine', 'jade');
app.use(logger('dev'));//日志
app.use(express.json());//json格式传输
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
// app.use(express.static(path.join(__dirname, 'public')));

app.use('/data', indexRouter);


// 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;