Is it possible for a 3rd party script to write cookies to the user's computer?
For example, if affiliate.example.org
includes:
<script type="text/javascript" src="http://me.example.com/cookiemonster.js"></script>
I want to provide an affiliate with a script, to hopefully write a cookie on their clients' machines; ideally we would want to control the script ourselves. However, before trying this, I just thought I would see if it is even possible.
Of course, the other option would be for us to provide the actual script for the affiliate to put directly onto their site.
Third-party cookies work by embedding JavaScript from one website into another. This enables them to transfer the habits of a user across multiple websites. Third-party cookies accumulate data gathered between browsing sessions and map a clear picture of the user.
Cookie data is automatically transmitted between the web browser and web server, so CGI scripts on the server can read and write cookie values that are stored on the client. As we'll see, JavaScript can also manipulate cookies using the cookie property of the Document object.
A third-party cookie is placed on a website by someone other than the owner (a third party) and collects user data for the third party. As with standard cookies, third-party cookies are placed so that a site can remember something about the user at a later time.
Yes, third party scripts can write cookies, and they will appear to belong to the domain of the page itself.
You can see this if you examine the cookies of any site using Google Analytics - the content comes from a third party (Google) but the _utm
prefix cookies will be on the hosting site's domain.
To write third-party cookies (i.e. where the cookie is on the domain of the third party) requires that the cookies be sent in the headers of a download from that third party, and not written by JS code.
What happenned when you tested it?
(yes, if the browser/user permits, it will record a cookie - but the domain of the cookie is determined by the domain the script was loaded from).
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