Flag evaluation reasons: Edge SDKs

This topic explains how to use the flag evaluation reason feature to get more information about the flag variations LaunchDarkly serves to contexts or users. This page covers edge sdks.

Edge SDKs

This feature is available for all of our edge SDKs:

• Akamai
• Cloudflare
• Fastly
• Vercel

Akamai

Expand Akamai code sample

The variationDetail method lets you evaluate a feature flag using the same parameters as you would for variation and receive more information about how the value was calculated.

The SDK returns the variation detail in an object that contains both the result value and a reason object. These tell you more information. For example, they can tell you if the flag individually targeted the context, or if the context matched one of the flag’s rules. It will also indicate if the flag returned the default value due to an error. You can examine the reason data programmatically.

Here is an example:

TypeScript

      const { value, variationIndex, reason } = await client.variationDetail(flagKey, context, false);

To learn more, read variationDetail, LDEvaluationDetail and LDEvaluationReason.

The LDClient also provides typed variation methods for type-safe usage in TypeScript: boolVariationDetail, stringVariationDetail, numberVariationDetail, jsonVariationDetail.

Every time you evaluate a flag, the SDK fetches the flag data from the EdgeKV store. Your Akamai resource tier may limit how many of these queries you can make while a single worker handler is being executed. To learn more, read Understand resource limits and caching options.

Cloudflare

Expand Cloudflare code sample

The variationDetail method lets you evaluate a feature flag using the same parameters as you would for variation and receive more information about how the value was calculated.

The SDK returns the variation detail in an object that contains both the result value and a “reason” object. These tell you, for instance, if the flag individually targeted the context or if the context matched one of the flag’s rules. It will also indicate if the flag returned the default value due to an error. You can examine the “reason” data programmatically, or, if you capture detailed analytics events for flags, view it with Data Export.

Here is an example:

TypeScript

      const { value, variationIndex, reason } = await client.variationDetail(flagKey, context, false);

To learn more, read variationDetail, LDEvaluationDetail and LDEvaluationReason.

The LDClient also provides typed variation methods for type-safe usage in TypeScript: boolVariationDetail, stringVariationDetail, numberVariationDetail, jsonVariationDetail.

Fastly

Expand Fastly code sample

The variationDetail method lets you evaluate a feature flag using the same parameters as you would for variation and receive more information about how the value was calculated.

The SDK returns the variation detail in an object that contains both the result value and a “reason” object. These tell you more information. For example, they can tell you if the flag individually targeted the context, or if the context matched one of the flag’s rules. It will also indicate if the flag returned the default value due to an error. You can examine the “reason” data programmatically, or, if you capture detailed analytics events for flags, view it with Data Export.

Here is an example:

TypeScript

      const { value, variationIndex, reason } = await client.variationDetail('example-flag-key', context, false);

To learn more, read variationDetail and LDEvaluationReason.

The LDClient also provides typed variation methods for type-safe usage in TypeScript: boolVariationDetail, stringVariationDetail, numberVariationDetail, jsonVariationDetail.

Vercel

Expand Vercel code sample

The variationDetail method lets you evaluate a feature flag using the same parameters as you would for variation and receive more information about how the value was calculated.

The SDK returns the variation detail in an object that contains both the result value and a “reason” object. These tell you more information. For example, they can tell you if the flag individually targeted the context, or if the context matched one of the flag’s rules. It will also indicate if the flag returned the default value due to an error. You can examine the “reason” data programmatically, or, if you capture detailed analytics events for flags, view it with Data Export.

Here is an example:

TypeScript

      const { value, variationIndex, reason } = await client.variationDetail(flagKey, context, false);

To learn more, read variationDetail, LDEvaluationDetail and LDEvaluationReason.

The LDClient also provides typed variation methods for type-safe usage in TypeScript: boolVariationDetail, stringVariationDetail, numberVariationDetail, jsonVariationDetail.