---
title: Track notification listener
slug: feature-experimentation/docs/track-notification-listener
docTags: 
createdAt: 2026-08-05T20:40:00.000Z
---

The track event method triggers this notification listener. Because the Feature Experimentation SDKs queue and batch events, there can be a delay between when the track event method captures an event and when the event is actually sent to Feature Experimentation as part of a batch. For more precise alignment with event batches, see [Log event notification listener](docId\:Rz6q1E5AKATNdC2U0P6ZK).

## Parameters

The following table lists the information provided to the track notification listener when it is triggered:

| field        | type   | description                                                                                                                                                                                                                                                                                  |
| ------------ | ------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `event key`  | String | The event key as you defined it in the Optimizely app.                                                                                                                                                                                                                                       |
| `user id`    | String | The user ID.                                                                                                                                                                                                                                                                                 |
| `attributes` | Map    | A map of custom key-value string pairs specifying attributes for the user that are used for [audience targeting](docId\:UDBvr5a8WHNkyOqzPhOr9). Non-string values are only supported in the SDK v3.0.0 and above for most SDKs. See [SDK compatibility matrix](docId:2shbZfPCkPAZ0mlZpL1TU). |
| `event tags` | Map    | A map of custom key-value pairs specifying tags for the tracked event. For information, see [Tag events](docId\:TPYh_YgbEQNnWIXKthzhl).                                                                                                                                                      |
| `event`      | Event  | The event object contains the `id`, `key` and `experiment ids`.                                                                                                                                                                                                                              |

## Examples

For code examples, see the following SDK documentation on notification listeners:

- [Android SDK](docId:7YBxDk67DRrkZf3FbyIJ-)
- [C# SDK](docId\:Ee1jEssfFPw17lJyVP9m9)
- [Flutter SDK](docId\:HK9-OAb_ZXtphGmvU8Uga)
- [Go SDK](docId\:t5MKaa3LIkBM5ovyv7XYn)
- [Java SDK](docId\:CaIM2oX09aWIajqNcz0Ct)
- [JavaScript SDK](docId\:iYEM6cOT51dak_I7ellNY) – SDK versions 6.0.0 and later.
- [JavaScript (Browser) SDK](docId\:qykXcla2WZgtq4LHGWSfU) – SDK versions 5.3.5 and earlier.
- [JavaScript (Node) SDK](docId\:qykXcla2WZgtq4LHGWSfU) – SDK versions 5.3.5 and earlier.
- [PHP SDK](docId\:B3h4PE4eFEjjhKpiue0N_)
- [React SDK](docId\:eyOn7CmG5jWwB3vIm7mt9)
- [React Native SDK](docId:04d5tm_qqBTXKMKKnh1rZ)
- [Ruby SDK](docId:0pKUE1RjpxrcY4xgjh1Y3)
- [Python SDK](docId\:EjbZOLZ2M6aN5QW0T1Ufy)
- [Swift SDK](docId\:olc5F0M6g6El8a0puGbRX)