Comment by downandout | Hacker News Reader

Comment by downandout | Hacker News Reader

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Something like that, yes. When you visit any URL on the site, we use javascript to rewrite the URL in the location bar with a shortened, unique, trackable URL. So we know both what URL you came in through, and the new URL that we then assigned to you. With this we can track every click all the way back up through the tree to the initial click, even if you just copy/paste the URL or hit the button on your phone to text the page to a given contact. Where possible, we also track any link preview engines that visit the URL, so we can usually tell not just that you shared, but how you shared (skype, telegram, iMessage, gmail, facebook, twitter, etc.).

I initially wrote this system so that I could retarget through Facebook ads people that had previously shared viral news articles, but now we have found great applications for it in ecommerce and lead gen as well.

You wouldn’t know who shared until someone doesn’t actually visit the shared link, right? Unless I’m misunderstanding something. Also I don’t see how you would build a custom audience on FB for the people who shared, e.g. by copy-pasting the URL from the location bar. I see how you would do it on some javascript event (e.g. page load, click on share button, etc.), but that’s not the same.

Correct, we don't know who shared until someone visits the link. But, we can build a custom audience after the fact because the Facebook retargeting pixel lets you pass an arbitrary ID of your choosing with each pixel load (the variable name is "extern_id" [1]). So when a click comes in on a given URL that we know had to have been shared, we know what extern_id we gave to Facebook for the original user that shared the link on the pixel fire back when they first visited the site. We can then build a custom audience using a list of those extern_id's for only people that have shared, after the fact.

https://developers.facebook.com/docs/marketing-api/audiences... - see "External Identifiers"

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