Javascript API在主站点上运行良好，但在外部服务器上无法运行

Question

This code can be used in conjuction with jQuery to embed a button on a page letting users share a link to my site.

<div class="button" data-text="Button text" data-url="http://externalserver.com">
</div>
<script src="http://mainserver.co.uk/api.js"></script>

The javascript file has to use xmlHTTPrequest to connect with php files to check whether or not you are logged in or not, and to then post the comment on my site. It is very simple, as all you need to do is click the button it creates. Or not.
Well, it works fine on any page on http://mainserver.co.uk , but on my external server, it just shows console errors such as

XMLHttpRequest cannot load filename. Origin http://externalserver.com is not allowed by Access-Control-Allow-Origin. 

Well I know this must be possible because twitter, google and facebook can all do it, so why can't I?

Ok, thanks. but this is still a problem.
Users have sessions on the mainsite which tells the webpage that they are logged in.
Using this code, I can test that.

<?php
session_start();
header("Access-Control-Allow-Origin: *");
if (isset($_SESSION["user"]))
{
    echo "0";
}
else
{
    echo "1";
}
?>

When I am logged in and run this code, it Returns 0 on the main site, but 1 on the external site, as if I am only logged in when testing on the main site

Answer 1

Origin http://externalserver.com is not allowed by Access-Control-Allow-Origin.

• its a cross domain ajax issue(Read more: same origin policy , cross domain requests )

If your JavaScript runs on example.com and the server you are requesting to is in example.net. Make sure it allows the page your js is running by this header

   <?php header('Access-Control-Allow-Origin: http://example.com/ajax.html'); ?>

or

   <?php header('Access-Control-Allow-Origin: *'); ?>

(the wildcard is going to allow any domain to send requests to your host. I recommend replacing the asterisk with a specific domain that you will be running scripts on)

Also you need to send Origin header from ajax to the server

Origin: http://example.com/ajax.html

XMLHttpRequest cannot load filename.

• is because you didn't specify full url in you ajax request. But it works with your main server because you run php in the same domain itself.