has been blocked by cors policy node js server code example

Example 1: nodejs CORS policy

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "YOUR-DOMAIN.TLD"); // update to match the domain you will make the request from
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
});

app.get('/', function(req, res, next) {
  // Handle the get for this route
});

app.post('/', function(req, res, next) {
 // Handle the post for this route
});

Example 2: Access to XMLHttpRequest has been blocked by CORS policy node js

/*
npm i cors
or
 yarn add cors
then in your node app
*/
const cors = require('cors');
const corsOptions ={
    origin:'http://localhost:3000', 
    credentials:true,            //access-control-allow-credentials:true
    optionSuccessStatus:200
}
app.use(cors(corsOptions));