The creation process of native Ajax
1. Create xhr core object
var xhr=new XMLHttpRequest();
2. Call open to prepare to send
-
Parameter 1: Request method
-
Parameter 2: Request address
-
Parameter three: true asynchronous, false synchronous
xhr.open('post','http://www.baidu.com/api/search',true)
3. If it is a post request, the request header must be set.
xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
4. Call send to send the request (if parameters are not needed, write null)
xhr.send('user=tom&age=10&sex=女')
5. Monitor the asynchronous callback onreadystatechange
-
Judging that the readyState is 4, the request is complete
-
Judging that the status code is 200, the interface request is successful
-
responeseText is the corresponding data. String type.
xhr.onreadystatechange=function(){
if(xhr.readyState==4){
if(xhr.status==200){
console.log(xhr.responseText);
var res=JSON.parse(xhr.responseText);
console.log(res);
if(res.code==1){
modal.modal('hide');
location.reload();
}
}
}
Note: If it is a post request, you want to send json format data.
Set request header
xhr.setRequestHeader('Content-Type', 'application/json')
open send data
xhr.open({
_id:xxx,user:xxxx,age:xxxx})
===================================================================
jsonp principle
Preface
The following is a use case of native jsonp. The backend uses a simple server built by node.
1. Front-end code
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.5.1/jquery.js"></script>
</head>
<body>
<script>
function showInfo123(data) {
console.log(data)
}
</script>
<script src="http://127.0.0.1:3000/getscript?callback=showInfo123"></script>
<!-- <script>
show()
</script> -->
<button id="btn">jsonp</button>
</body>
</html>
<script>
$('#btn').click(function(){
var frame = document.createElement('script');
frame.src = 'http://localhost:3000/getscript?callback=showInfo123';
$('body').append(frame);
})
</script>
2. Backend code node.js
// 导入 http 内置模块
const http = require('http')
// 这个核心模块，能够帮我们解析 URL地址，从而拿到 pathname query
const urlModule = require('url')
// 创建一个 http 服务器
const server = http.createServer()
// 监听 http 服务器的 request 请求
server.on('request', function (req, res) {
// const url = req.url
const {
pathname: url, query } = urlModule.parse(req.url, true)
if (url === '/getscript') {
// 拼接一个合法的JS脚本，这里拼接的是一个方法的调用
// var scriptStr = 'show()'
var data = {
name: 'xjj',
age: 18,
gender: '女孩子'
}
var scriptStr = `${
query.callback}(${
JSON.stringify(data)})`
// res.end 发送给 客户端， 客户端去把 这个 字符串，当作JS代码去解析执行
res.end(scriptStr)
} else {
res.end('404')
}
})
// 指定端口号并启动服务器监听
server.listen(3000, function () {
console.log('server listen at http://127.0.0.1:3000')
})
Words Summary: Principles of JSONP
Ajax requests are affected by the same-origin policy and cross-domain requests are not allowed. We use the src attribute of the script tag to not be restricted by the same-origin policy. Using this feature jsonp requires the following steps:
1, dynamic creation
<script></script>(document.createElement('script'))
2, src attribute set, (src parameters to be includedcallback=fn) cross-domain request
3,<script></script>added to the page executing（body.appendChild('script')）
4, to define in advance the pagecallback。
5, the rear end of the callback function returns the execution parameters and wrappedcallback(data)
Remarks:
The server no longer returns the data in JSON format, but returns the callback function package data (fn({name:'tom',age:18})), which is called in src, thus achieving cross-domain.
CORS setup cross-domain request
//设置允许跨域的域名，*代表允许任意域名跨域 CORS跨域
res.setHeader("Access-Control-Allow-Origin","http://127.0.0.1:3003");
How to set up proxy cross-domain in vue-cli
In the vue component:
fn(){
this.$axios.get('/api/api/v1/home').then(res=>{
console.log(res.data);
})
}
module.exports={
devServer: {
proxy:{
'/api':{
target:'http://127.0.0.1:3002/',//跨域请求资源地址
ws:false,//是否启用websockets
/*开启代理：在本地会创建一个虚拟服务端，然后发送请求的数据，并同时接收请求的数据，
这样服务端和服务端进行数据的交互就不会有跨域问题*/
changeOrigin:true
pathRewrite:{
'^/api':''//注册全局路径
}
}
}
}
}