前端学习遇到的一些小坑

1.Access to XMLHttpRequest at ‘http://127.0.0.1:8000/delay’ from origin ‘http://localhost:63342’ has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource.
请求接口写的xhr.open(‘GET’,‘http://127.0.0.1:8000/delay’);，后台响应应该对应GET或者ALL，直接复制粘贴的post忘记改了，应该是

app.all('/delay',(request,response)=>{
    response.setHeader('Access-Control-Allow-Origin','*');
    response.setHeader('Access-Control-Allow-Headers','*');
    response.send("hello12");