!DOCTYPE html>
html lang="en">
head>
 meta charset="UTF-8">
 meta name="viewport" content="width=device-width, initial-scale=1.0">
 title>Document/title>
/head>
body>
 script>
 /**
  * type: get/post
  * url: http://localhost:3000 http://localhost:3000/details http://localhost:3000/users
  * data: lid=5 / uname=liliupwd=123456
  * dataType: '' / 'json', 如果服务端返回的是json格式字符串，就通过dataType通知ajax函数自动转换为对象
  * **/
 ajax({
  type: 'get',
  url: 'http://localhost:3000',
  dataType: 'json'
 })
 // data 不写在解构时值默认为 data: undefined
 ajax({
  type: 'get',
  url: 'http://localhost:3000/details',
  data: 'lid=0',
  dataType: 'json'
 })
 ajax({
  type: 'post', 
  url: 'http://localhost:3000/users', 
  data: 'uname=liliupwd=123456',
 }).then(function(res){
  alert(res)
 })
 // dataType 不写在解构时值默认为 dataType: undefined

 function ajax({type, url,data, dataType}){
  return new Promise(function(open){
  var xhr = new XMLHttpRequest()
  xhr.onreadystatechange = function(){
   if(xhr.readyState === 4  xhr.status === 200){
   if(dataType === 'json'){
    var res = JSON.parse(xhr.responseText)
   }else{
    var res = xhr.responseText
   }
   console.log(res)
   open(res)
   }
  }

  if(type === 'get'  data !== undefined){
   url += `?${data}`
  }
  xhr.open(type, url, true)
  xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded')

  if(type === 'get'){
   xhr.send()
  }else{
   xhr.send(data)
  }
  })
 }
 /script>
/body>
/html>

!DOCTYPE html>
html lang="en">
head>
 meta charset="UTF-8">
 meta name="viewport" content="width=device-width, initial-scale=1.0">
 title>Document/title>
/head>
body>
 script>
 var xhr = new XMLHttpRequest()
 xhr.onreadystatechange = function(){
  if(xhr.readyState === 4  xhr.status === 200){
  console.log(xhr.responseText)
  }
 }
 xhr.open('get', 'http://localhost:3000', true)
 xhr.send()
 /script>
/body>
/html>

// index.js
var express = require('express');
var router = express.Router();

/* GET home page. */
var products = [
 {
 lid:1,
 pname:'笔记本',
 price:3400
 },
 {
 lid:2,
 pname:'手机',
 price:5400
 },
 {
 lid:3,
 pname:'iPad',
 price:6400
 }
]

router.get('/', function(req, res, next) {
 res.send(products)
});

router.get('/details', function(req, res, next){
 var lid = req.query.lid
 res.send(products[lid])
})

module.exports = router;

// user.js
var express = require('express');
var router = express.Router();

/* GET users listing. */
router.post('/', function(req, res, next) {
 var uname = req.body.uname
 var upwd = req.body.upwd
 if(uname === 'lili'  upwd === '123456'){
 res.send('登陆成功')
 }else{
 res.send({
  code: 0,
  message: '用户名或密码错误'
 })
 }
});

module.exports = router;