node_中间件

执行命令：

express --view=ejs midapp

cnpm install

nodemon ./bin/www

express.urlencoded（）：解析body的函数

express.Router();：实例化路由模块，此路由模块相当于一个小的app实例

跨域：域名或者端口不同都算跨域

跨域问题解决：服务器设定允许访问即可（设置Access-Control-Allow-Origin请求头）

// 允许前端跨域请求的中间件
api.use((req, res, next) => {
    // 允许所有源
    res.append('Access-Control-Allow-Origin', "*");
    // 允许所有请求类型
    res.append('Access-Control-Allow-Content-Type', "*");
    next();
})

1.应用层中间件

app.js

var express = require('express');
var path = require('path');

var app = express();
let router1 = require('./routes/mall');
let api = require('./routes/api');

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

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

// 添加中间件
// 如果不写next,将被截获在此,不能继续向下执行
// 一般中间件是处理req,或者res的
app.use(function (req, res, next) {
  res.addNum = function (a, b) {
    return a + b;
  }
  console.log("访问任何页面,此函数都会被调用");
  next();
})

// 封装lcQuery中间件
app.use(function (req, res, next) {
  try {
    let splitRes = req.url.split('?');
    if (splitRes.length > 0) {
      let queryStr = req.url.split('?')[1];
      if (queryStr == undefined) {
        next();
      }
      // 对表单提交的键值对进行分割
      let keyValueArr = queryStr.split('&');
      // 设置一个query对象，将键值对以对象的属性形式进行保存
      let query = {};
      keyValueArr.forEach(function (item, i) {
        // searchKey=admin,进行分割
        let key = item.split('=')[0];
        let value = item.split('=')[1];
        query[key] = value;

      })
      req.lcQuery = query;
      next();

    } else {
      next();
    }
  } catch (error) {}
})

app.get('/', (req, res) => {
  console.log(req.lcQuery);
  res.send("首页" + res.addNum(1, 2));
})


app.use('/mall', router1);
app.use('/api', api);

module.exports = app;

2.路由中间件

mall.js

let express = require('express');
// 实例化路由模块
let router1 = express.Router();
router1.use(function (req, res, next) {
    console.log("判断用户是不是商城用户");
    next();
})
router1.get('/', (req, res) => {
    res.send("商城首页");
})
router1.get('/list', (req, res) => {
    res.send("商城产品列表页");
})

module.exports = router1;

api.js

let express = require('express');
let sqlQuery = require('../lcMysql');
// 实例化路由模块
// 提供Ajax请求的接口
let api = express.Router();

// 允许前端跨域请求的中间件
api.use((req, res, next) => {
    // 允许所有源
    res.append('Access-Control-Allow-Origin', "*");
    // 允许所有请求类型
    res.append('Access-Control-Allow-Content-Type', "*");
    next();
})

async function getCataory() {
    let sqlStr = "select * from cataory";
    let result = await sqlQuery(sqlStr);
    return Array.from(result);
}

// 提供什么分类下的，第N页book的数据
api.get('/book/cataory/:cid/page/:pid', async (req, res) => {
    let page = parseInt(req.params.pid);
    let cid = req.params.cid;
    let strSql;
    let arr;
    let result;
    if (cid == 0) {
        strSql = "select id,bookname,bookimg,author,cataory from book limit ?,1";
        arr = [(page - 1) * 1]; //*num:就是乘每页的书本数，由数据库语句的limit的第二位决定
        result = await sqlQuery(strSql, arr);
    } else {
        strSql = "select id,bookname,bookimg,author,cataory from book WHERE cataory in (SELECT cataory from cataory WHERE id=?)limit ?,1";
        arr = [cid, (page - 1) * 1]; //*num:就是乘每页的书本数，由数据库语句的limit的第二位决定
        result = await sqlQuery(strSql, arr);
    }


    // 获取总页数
    let strSql1 = "select count(id) as num from book WHERE cataory in (SELECT cataory from cataory WHERE id=?)";
    let result1 = await sqlQuery(strSql1, arr);
    let pageAll = Math.ceil(result1[0].num / 1);
    let startPage = (page - 4) < 1 ? 1 : (page - 4);
    let endPage = (page + 5) > pageAll ? pageAll : (page + 5);

    let options = {
        books: Array.from(result),
        cataorys: await getCataory(),
        pageAll,
        page,
        cid,
        startPage,
        endPage
    }

    res.json(options);
})
api.get('/list', (req, res) => {
    res.send("商城产品列表页");
})

module.exports = api;

api应用的book的history

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="js/jquery.min.js"></script>
</head>

<body>
    <h1>历史相关书籍</h1>
    <script>
        let httpUrl = '/api/book/cataory/3/page/1';
        $.ajax(httpUrl).then(function (res) {
            console.log(res);
            res.books.forEach((item, i) => {
                $('body').append("<h2>" + item.bookname + "<h2>");
            })
        })
    </script>
</body>

</html>

1.应用层中间件

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