Enable CORS while an XMLHttpRequest error occurs in flutter web

For enabling cors on my server and to resolve XMLHttpRequest error in flutter web

I am using this in my .htaccess file for allowing access to certain domains only

 <ifModule mod_headers.c>
    SetEnvIf Origin "http(s)?://(localhost:25120|domain.com|domain2.com)$" AccessControlAllowOrigin=$0
    Header add Access-Control-Allow-Origin %{AccessControlAllowOrigin}e env=AccessControlAllowOrigin
    Header always set Access-Control-Allow-Methods: "GET,POST,OPTIONS,DELETE,PUT"
 </ifModule>    

For anyone who is using node.js server, enable cors support in your server side code.

1. npm i cors express
2. In index.js or server.js -

const express = require("express");

const app = express();
var cors = require("cors");
app.use(cors()); 

This should fix cors issue with flutter web

if you have experienced something like that, and the server has added Access-Control-Allow-Origin but is still blocked by CORS, try checking the function (if you use the function to CRUD with postrgresql) because my problem is solved when I fix the function

Disabling CORS policy on Chrome is a temporary solution. It's just frustrating that you have to manually call it before starting Chrome every. single. time. Disable same origin policy in Chrome

Vicky Salunkhe described in his answer one option with .htaccess very well. I found that and an alternative if you try to read from a server where you are running a php script yourself here. If you want to read some data from a MySQL database and return it as json with the right CORS setting, you could try this:

<?php

header("Access-Control-Allow-Headers: Authorization, Content-Type");
header("Access-Control-Allow-Origin: *");
header('content-type: application/json; charset=utf-8');


$host_name = '...';
$database = '...';
$user_name = '...';
$password = '...';

$link = new mysqli($host_name, $user_name, $password, $database);
if ($link->connect_error) {    
    die('<p>Failed to connect to MySQL: ' . $link->connect_error .
     '</p>');
}
$link->set_charset('utf8mb4');

$sql = "...";
$result = $link->query($sql);
$result = $link->query($sql);
$data = $link->query($sql)->fetch_all(MYSQLI_ASSOC);
echo json_encode($data);