Express框架

npm安装express包
可以设立一个服务器 ，但是你直接打开回显示404 ，因为没有设置路由

const express = require('express');
const app = express();
const PORT = 4001;
app.listen(PORT, () => {
  console.log(`Server is listening on port ${PORT}`);
});

请求方式

get获取
put更新
post添加

路由及方法

tips:即使有两条以/expressions 为路径的路由，第一个匹配并发送响应，第二个路由将被忽略。

const express = require('express');
const app = express();
const {
  getElementById,
  getIndexById,
  updateElement,
  seedElements,
  createElement
} = require('./utils');
const PORT = process.env.PORT || 4001;
app.use(express.static('public'));
const expressions = [];
seedElements(expressions, 'expressions');
const animals = [];
seedElements(animals, 'animals');
// Get all expressions
app.get('/expressions', (req, res, next) => {
  res.send(expressions);
});
// Get a single expression 动态路由
app.get('/expressions/:id', (req, res, next) => {
  const foundExpression = getElementById(req.params.id, expressions);
  if (foundExpression) {
    res.send(foundExpression);
  } else {
    res.status(404).send();
  }
});
// Update an expression 更新
app.put('/expressions/:id', (req, res, next) => {
  const expressionIndex = getIndexById(req.params.id, expressions);
  if (expressionIndex !== -1) {
    updateElement(req.params.id, req.query, expressions);
    res.send(expressions[expressionIndex]);
  } else {
    res.status(404).send();
  }
});
// Create an expression 添加
app.post('/expressions', (req, res, next) => {
  const receivedExpression = createElement('expressions', req.query);
  if (receivedExpression) {
    expressions.push(receivedExpression);
    res.status(201).send(receivedExpression);
  } else {
    res.status(400).send();
  }
});
// Delete an expression 删除
app.delete('/expressions/:id', (req, res, next) => {
  const expressionIndex = getIndexById(req.params.id, expressions);
  if (expressionIndex !== -1) {
    expressions.splice(expressionIndex, 1);
    res.status(204).send();
  } else {
    res.status(404).send();
  }
});
app.listen(PORT, () => {
  console.log(`Server is listening on ${PORT}`);
});

路由器 router

好处：划分功能模块 可以省下前缀

const express = require('express');
const {
  getElementById,
  getIndexById,
  updateElement,
  seedElements,
  createElement
} = require('./utils');
let expressions = [];
seedElements(expressions, 'expressions');
expressionsRouter = express.Router();
// Get all expressions
expressionsRouter.get('/', (req, res, next) => {
  res.send(expressions);
});
// Get a single expression
expressionsRouter.get('/:id', (req, res, next) => {
  const foundExpression = getElementById(req.params.id, expressions);
  if (foundExpression) {
    res.send(foundExpression);
  } else {
    res.status(404).send();
  }
});
// Update an expression
expressionsRouter.put('/:id', (req, res, next) => {
  const expressionIndex = getIndexById(req.params.id, expressions);
  if (expressionIndex !== -1) {
    updateElement(req.params.id, req.query, expressions);
    res.send(expressions[expressionIndex]);
  } else {
    res.status(404).send();
  }
});
// Create an expression
expressionsRouter.post('/', (req, res, next) => {
  const receivedExpression = createElement('expressions', req.query);
  if (receivedExpression) {
    expressions.push(receivedExpression);
    res.status(201).send(receivedExpression);
  } else {
    res.status(400).send();
  }
});
// Delete an expression
expressionsRouter.delete('/:id', (req, res, next) => {
  const expressionIndex = getIndexById(req.params.id, expressions);
  if (expressionIndex !== -1) {
    expressions.splice(expressionIndex, 1);
    res.status(204).send();
  } else {
    res.status(404).send();
  }
});
module.exports = expressionsRouter;

中间件

避免重复代码
降低复杂性
中间件在这接受请求和发送响应的边界上运行。
在 Express 中，中间件是一个函数。中间件可以对请求和响应对象执行逻辑，例如：检查请求，根据请求执行一些逻辑，向响应附加信息，向响应附加状态，将响应发送回用户，或简单地传递对另一个中间件的请求和响应。中间件可以做这些事情的任何组合，也可以做任何其他 Javascript 函数可以做的事情