Mixpanel server-side proxy to bypass blockers
(2 minute read)
For my new startup - Kickback - we decided to launch a static landing page as a precursor to the full product (which will be ready in a few weeks). On our landing page we have a call-to-action button near the bottom for users who wish to register their interest in our service:
Naturally, we wanted to track these clicks and visits through analytics, and we chose Mixpanel. Unfortunately, Brave browser and some other ad blockers block the Mixpanel library from even loading. Looking at Mixpanel's own documentation on this issue, it seemed clear to me that a server-side proxy was the only solution to this problem.
Thus I went ahead and coded https://github.com/noblocknoparty/analytics-server.
It's written using Koa, my goto Node.js framework.
Upon startup this downloads the current live Mixpanel JS library into memory. When a request comes in for /client.js it first extracts the origin of the request and then uses string replacement to replace the api_host config variable in the Mixpanel JS code to point to the proxy server at the given origin address.
For example, if the proxy server is running at https://mproxy.com, then a request to http://mproxy.com/client.js will return the Mixpanel JS library but with the api_host value set to https://mproxy.com instead of https://api.mixpanel.com, thus causing all subsequent analytics requests to be sent to the proxy server.
The proxy server then forwards all incoming requests from the client library onto as-is (including headers) onto Mixpanel.
It also sets the X-Forwarded-For to the client browser's IP address so that Mixpanel will still resolve the right location for the user.
The above proxy server can be served up on any domain, it's not specific to our app. To use it with Mixpanel, follow the standard Mixpanel setup instructions and then add the following before the Mixpanel block: