access-control-allow-origin javascript code example

Example 1: access-control-allow-origin nodejs express

// Add headers
app.use(function (req, res, next) {

    // Website you wish to allow to connect
    res.setHeader('Access-Control-Allow-Origin', 'http://localhost:8888');

    // Request methods you wish to allow
    res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');

    // Request headers you wish to allow
    res.setHeader('Access-Control-Allow-Headers', 'X-Requested-With,content-type');

    // Set to true if you need the website to include cookies in the requests sent
    // to the API (e.g. in case you use sessions)
    res.setHeader('Access-Control-Allow-Credentials', true);

    // Pass to next layer of middleware
    next();
});

Example 2: access-control-allow-origin

Access-Control-Allow-Origin: *

Example 3: cross origin even with allow header

header('Access-Control-Allow-Origin: http://localhost:8100');
header ("Access-Control-Expose-Headers: Content-Length, X-JSON");
header ("Access-Control-Allow-Methods: GET, POST, PATCH, PUT, DELETE, OPTIONS");
header ("Access-Control-Allow-Headers: Content-Type, Authorization, Accept, Accept-Language, X-Authorization");
header('Access-Control-Max-Age: 86400');

if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
    // The request is using the POST method
    header("HTTP/1.1 200 OK");
    return;

}

Example 4: Access to XMLHttpRequest at 'http://localhost/MySQL_pracs/InsertUser.php' from origin 'http://localhost:4200' has been blocked by CORS policy: Request header field content-type is not allowed by Access-Control-Allow-Headers in preflight response.

//Access to XMLHttpRequest at 'http://localhost/[api path].php' from origin 'http://localhost:4200' has been blocked by CORS policy: Request header field content-type is not allowed by Access-Control-Allow-Headers in preflight response.

//The error is simply saying that "Content-Type" is missing from "Access-Control-Allow-Headers".

//Therefore we need to add "Content-Type" to "Access-Control-Allow-Headers".

<?php 
header('Access-Control-Allow-Headers: Content-Type');
-----
?>

Example 5: what is cors

“CORS” stands for Cross-Origin Resource Sharing. 
It allows you to make requests from one website to another website 
in the browser, which is normally prohibited by another browser policy 
called the Same-Origin Policy (SOP).

Example 6: header access-control particular domain

Access-Control-Allow-Origin: http://siteA.com

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