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110 lines
4.8 KiB
Markdown
110 lines
4.8 KiB
Markdown
---
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title: Impression Data
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---
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:::note Availability
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**Version**: `4.7+`. Requires [SDK compatibility](../reference/sdks/index.md#server-side-sdk-compatibility-table).
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:::
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Unleash can provide you with **impression data** about the flags in your application. Impression data contains information about a specific feature flag activation check: The client SDK will emit an **impression event** when it calls `isEnabled` or `getVariant`. Some front-end SDKs emit impression events only when a flag is enabled.
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:::caution Front-end SDKs and disabled flags
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Older versions of the front-end SDKs and other SDKs that connect the [Unleash proxy](../generated/unleash-proxy.md) or the [Unleash front-end API](../reference/front-end-api.md) would **not** emit impression events when a flag is disabled.
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This is because impression data is a **per-flag** setting and the Proxy and front-end API only transmit information about flags that are enabled. As such, the SDK will never know that it should emit an impression event if a flag is disabled.
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Some of the front-end SDKs now include a include a configuration property that lets you turn on impression data for all flags regardless of whether they're enabled or not.
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:::
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Impression data was designed to make it easier for you to **collect analytics data**, **perform A/B tests**, and **enrich experiments** in your applications. It contains information about the feature flag and the related [Unleash Context](../reference/unleash-context.md).
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Impression data is **opt-in on a per-flag basis**. Unleash will not emit impression events for flags not marked as such. Once you've turned impression data on for a flag, you can start listening for impression events in your client SDK.
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## Impression event data
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There's two types of impression events you can listen for:
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- [`isEnabled` events](#example-isenabled)
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- [`getVariant` events](#example-getvariant)
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The `getVariant` event contains all the information found in an `isEnabled` event in addition to extra data that's only relevant to `getVariant` calls.
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This table describes all the properties on the impression events:
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| Property name | Description | Event type |
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| --- | --- | --- |
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| `eventType` | The type of the event: `isEnabled` or `getVariant` | All |
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| `eventId` | A globally unique id (GUID) assigned to this event. | All |
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| `context` | A representation of the current [Unleash Context](../reference/unleash-context.md). | All |
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| `enabled` | Whether the flag was enabled or not at when the client made the request. | All |
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| `featureName` | The name of the feature flag. | All |
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| `variant` | The name of the active variant | `getVariant` events only |
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### Example `isEnabled` event {#example-isenabled}
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```js
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{
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eventType: 'isEnabled',
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eventId: '84b41a43-5ba0-47d8-b21f-a60a319607b0',
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context: {
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sessionId: 54085233,
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appName: 'my-webapp',
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environment: 'default'
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},
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enabled: true,
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featureName: 'my-feature-flag',
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}
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```
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### Example `getVariant` event {#example-getvariant}
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```js
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{
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eventType: 'getVariant',
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eventId: '84b41a43-5ba0-47d8-b21f-a60a319607b0',
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context: {
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sessionId: 54085233,
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appName: 'my-webapp',
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environment: 'default'
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},
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enabled: true,
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featureName: 'my-feature-flag',
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variant: 'variantA'
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}
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```
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## Enabling impression data
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Impression data is strictly an **opt-in** feature and must be enabled on a **per-flag basis**. You can enable and disable it both when you create a flag and when you edit a flag.
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You can enable impression data via the impression data flag in the admin UI's flag creation form. You can also go via the [the API, using the `impressionData` option](/reference/api/legacy/unleash/admin/features-v2.md#create-toggle). For more detailed instructions, see [the section on enabling impression data in the how-to guide for capturing impression data](../how-to/how-to-capture-impression-data.mdx#step-1).
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## Example setup
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The exact setup will vary depending on your [client SDK](../reference/sdks/index.md). The below example configures the [Unleash Proxy client../reference/sdks/javascript-browser) to listen for impression events and log them to the console. If "my-feature-flag" is configured to emit impression data, then it will trigger an impression event as soon as Unleash is ready.
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```js
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const unleash = new UnleashClient({
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url: 'https://eu.unleash-hosted.com/hosted/proxy',
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clientKey: 'your-proxy-key',
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appName: 'my-webapp',
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});
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unleash.start();
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unleash.on('ready', () => {
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unleash.isEnabled('my-feature-flag');
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});
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unleash.on('impression', (event) => {
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// Capture the event here and pass it to internal data lake or analytics provider
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console.log(event);
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});
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```
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