The thing is I m using a middleware for A B testing and I m

Question

The thing is I m using a middleware for A B testing and I m not exactly sure how to get the Mixpanel distinct id in this middleware or even if I can access it

fresh-football-47124 · Answer

Hi Cezar

fresh-football-47124 · Answer

let me find you my sample code for Mixpanel

fresh-football-47124 · Answer

```mixpanel init 6a37b4557 replace debug true loaded function mx growthbook setAttributes growthbook getAttributes id mx get distinct id ```

bumpy-student-89073 · Answer

Here s what I ve got

bumpy-student-89073 · Answer

I m initializing the Mixpanel lib using the `mixpanel browser` package in the ` app js` file

bumpy-student-89073 · Answer

which I think is already too late

fresh-football-47124 · Answer

you can update the attributes with setAttributes which replaces all the attributes

fresh-football-47124 · Answer

Did you try that sample code

bumpy-student-89073 · Answer

oh so if I do this in ` app js` ```const growthbook = new GrowthBook attributes id visitor id features await getFeatures trackingCallback experiment result = gt mixpanel track $experiment started Experiment name experiment key Variant name result variationId ```

bumpy-student-89073 · Answer

I did try it but it didn t work

fresh-football-47124 · Answer

is that the only attribute your adding

bumpy-student-89073 · Answer

well yeah for now just trying to set it up

bumpy-student-89073 · Answer

this code ``` const growthbook = new GrowthBook attributes id visitor id features await getFeatures trackingCallback experiment result = gt mixpanel track $experiment started Experiment name experiment key Variant name result variationId ``` gives me an error ```TypeError Cannot read properties of undefined reading disable all events at MixpanelLib event is disabled webpack internal middleware node modules mixpanel browser dist mixpanel cjs js 5561 21 at MixpanelLib eval webpack internal middleware node modules mixpanel browser dist mixpanel cjs js 4776 14 at MixpanelLib eval as track webpack internal middleware node modules mixpanel browser dist mixpanel cjs js 2789 27 at Object trackingCallback webpack internal middleware pages middleware ts 45 69 at GrowthBook track webpack internal middleware node modules growthbook growthbook dist esm GrowthBook js 498 20 at GrowthBook run webpack internal middleware node modules growthbook growthbook dist esm GrowthBook js 473 10 at GrowthBook run webpack internal middleware node modules growthbook growthbook dist esm GrowthBook js 126 25 at GrowthBook evalFeature webpack internal middleware node modules growthbook growthbook dist esm GrowthBook js 311 26 at GrowthBook feature webpack internal middleware node modules growthbook growthbook dist esm GrowthBook js 220 17 at Object middleware as handler webpack internal middleware pages middleware ts 53 20 ```

bumpy-student-89073 · Answer

I m guessing the `mixpanel` object doesn t make sense in the context of a middleware

fresh-football-47124 · Answer

could be

fresh-football-47124 · Answer

This is how I got it working in my NextJS app using app tsx ```const growthbook = new GrowthBook trackingCallback experiment result = gt mixpanel track Experiment Viewed Experiment Id experiment key Variant Id result variationId mixpanel init 60c30 b4557 debug true loaded function mx growthbook setAttributes growthbook getAttributes id mx get distinct id const FEATURES ENDPOINT = <http localhost 3100 api features key dev e 5365> function MyApp Component pageProps AppProps useEffect = gt Load feature definitions from API fetch FEATURES ENDPOINT then res = gt res json then json = gt growthbook setFeatures json features TODO replace with real targeting attributes growthbook setAttributes id 432 deviceId foo company foo loggedIn true employee true country foo browser foo url foo return lt GrowthBookProvider growthbook= growthbook gt lt Component pageProps gt lt GrowthBookProvider gt ``` But I haven t tested using the middleware

fresh-football-47124 · Answer

< future teacher 7046> can help you when he s around

bumpy-student-89073 · Answer

It seems Mixpanel has another package for Node but using that I get an error as well

bumpy-student-89073 · Answer

```You re using a Node js module events which is not supported in the Edge Runtime ```

future-teacher-7046 · Answer

I can t find very much about using Mixpanel from within Next js middleware so not sure if that s possible I also don t think you ll be able to get the distinct id there easily

future-teacher-7046 · Answer

One option is to use your own visitor id cookie for assigning variations Then pass the result to the front end in a cookie and track it in Mixpanel when the page loads

bumpy-student-89073 · Answer

Would creating 2 instances of GrowthBook work Like this in the middleware ``` Get existing visitor cookie or create a new one let visitor id = req cookies COOKIE || crypto randomUUID const growthbook = new GrowthBook attributes id visitor id features await getFeatures ``` and then in ` app js` ```new GrowthBook attributes id mixpanel id trackingCallback experiment result = gt mixNode track $experiment started Experiment name experiment key Variant name result variationId ```

future-teacher-7046 · Answer

The tracking callback only fires on the same GrowthBook instance where you evaluate a feature value

bumpy-student-89073 · Answer

oh so it wouldn t work

bumpy-student-89073 · Answer

gt One option is to use your own visitor id cookie for assigning variations Then pass the result to the front end in a cookie and track it in Mixpanel when the page loads Do you have an example of this

bumpy-student-89073 · Answer

I can t visualize how that works

future-teacher-7046 · Answer

In your middleware set a cookie with the experiment key and assigned variation ```res cookie GB EXPERIMENTS JSON stringify key my experiment variationId 1 ``` Then in your ` app js` track in mixpanel ```useEffect = gt const experiments = document cookie GB EXPERIMENTS if experiments return const parsed = JSON parse experiments if parsed return parsed forEach res = gt mixpanel track $experiment started Experiment name res key Variant name res variationId ```

bumpy-student-89073 · Answer

Cool that seems to work Thank you