Evaluation reasons and error codes

When you evaluate a flag using the binding's *Details methods or the OpenFeature SDK, the response includes a reason field that explains why a particular value was returned. If an error occurs, the response includes an errorCode field.

Evaluation reasons

Reason	Description
`TARGETING_MATCH`	A targeting rule's conditions matched the evaluation context, and the rule's variation was returned.
`SPLIT`	A targeting rule with a percentage rollout matched. The user fell within the rollout percentage and received the rule's variation.
`DEFAULT`	No targeting rule matched the evaluation context. The flag's default variation was returned.
`DISABLED`	The flag is disabled. The default variation was returned regardless of targeting rules.

Error codes

When an evaluation error occurs, the method returns the default value you provided. The *Details methods include additional metadata about the error.

Error code	Description
`TYPE_MISMATCH`	The flag's variation type does not match the requested type. For example, calling `getBooleanValue` on a flag whose variation is a string. The default value is returned.
`GENERAL`	An unexpected error occurred during evaluation (for example, a network failure). The default value is returned.
`FLAG_NOT_FOUND`	The specified flag key does not exist in the app. The default value is returned.

Example

The following example inspects evaluation details returned by getBooleanDetails:

JavaScript
TypeScript

const details = await env.FLAGS.getBooleanDetails("my-feature", false, {
  userId: "user-42",
});

switch (details.reason) {
  case "TARGETING_MATCH":
    console.log(`Matched targeting rule, variant: ${details.variant}`);
    break;
  case "SPLIT":
    console.log(`Included in rollout, variant: ${details.variant}`);
    break;
  case "DEFAULT":
    console.log("No rule matched, using default variation");
    break;
  case "DISABLED":
    console.log("Flag is disabled");
    break;
}

if (details.errorCode) {
  console.error(
    `Evaluation error: ${details.errorCode} - ${details.errorMessage}`,
  );
}

const details = await env.FLAGS.getBooleanDetails("my-feature", false, {
  userId: "user-42",
});

switch (details.reason) {
  case "TARGETING_MATCH":
    console.log(`Matched targeting rule, variant: ${details.variant}`);
    break;
  case "SPLIT":
    console.log(`Included in rollout, variant: ${details.variant}`);
    break;
  case "DEFAULT":
    console.log("No rule matched, using default variation");
    break;
  case "DISABLED":
    console.log("Flag is disabled");
    break;
}

if (details.errorCode) {
  console.error(
    `Evaluation error: ${details.errorCode} - ${details.errorMessage}`,
  );
}