作为一个前端，没有后端数据的时候，自己模拟，就是最好的结局，我常用的就是两种：
1.postman进行后端模拟，在此就不进行多余叙述，
2.node后端，用express当中间件，也是问题的源头。
在进行请求时，终端报错为：
has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.
我用的编译器是vscode，它的默认编译端口是5500，而我后台路径端口是8089，导致CORS没有通过，也就是跨域问题，直接看代码
let obj = document.getElementById('ref');
obj.addEventListener('click', ajax)
// 利用Ajax进行数据请求
function ajax() {
console.log('ll');
let xhr = new XMLHttpRequest();
xhr.onreadystatechange = function () {
if (xhr.readyState == 4) {
if ((xhr.status >= 200 && xhr.status < 300) || xhr.status == 304) {
console.log(xhr.responseText);
} else {
console.log("Request was unsuccessful" + xhr.status);
}
}
}
xhr.open("get", "http://127.0.0.1:8089/api/userId", true);
xhr.send(null)?后台数据
const exp = require("express");
const app = exp();
app.listen(8089, () => {
console.log('Server listen http://127.0.0.1:8089')
})
app.use((req, rsp, next) => {
rsp.setHeader('Access-Control-Allow-Origin', '*')
next()
})
// app.all(" * ", function(req, res, next) {undefined
// res.header('Access-Control-Allow-Origin', " * ");
// res.header('Access-Control-Allow-Headers', 'Content-Type,Content-Length, Authorization, Accept,X-Requested-With');
// res.header('Access-Control-Allow-Methods','PUT,POST,GET,DELETE,OPTIONS');
// res.header('X-Powered-By','3.2.1')
// if(req.method=='OPTIONS') res.send(200);//让options请求快速返回/
// else next();
// });
app.get('/api/userId', (req, rsp) => {
console.log('你请求的地址是/api/hello!', req.name);
// rsp.send({name:'baobosun',age:47,sex:'男'});
// rsp.setHeader('Access-Control-Allow-Origin', '*')
OptMysql(rsp)
// rsp.send(OptMysql())
})
//做数据库连接
function OptMysql(res) {
const mysql = require('mysql');
var par = null
var connection = mysql.createConnection({
host: "127.0.0.1",
port: 3306,
user: 'root',
password: 'root',
database: 'student'
});
connection.connect();
// 查询数据
connection.query("select * from info", function (err, results, fields) {
if (err) throw err;
// console.log('results:', results);
res.send(results)
});
}
解决的问题的办法就是在app.use()进行过滤的时候，添加请求头。
rsp.setHeader('Access-Control-Allow-Origin', '*')
