feat: add binding for flag evaluation

types/defines/flags.d.ts

@@ -0,0 +1,145 @@
+/**
+ * Evaluation context for targeting rules.
+ * Keys are attribute names (e.g. "userId", "country"), values are the attribute values.
+ */
+export type EvaluationContext = Record<string, string | number | boolean>;
+
+export interface EvaluationDetails<T> {
+  flagKey: string;
+  value: T;
+  variant?: string | undefined;
+  reason?: string | undefined;
+  errorCode?: string | undefined;
+  errorMessage?: string | undefined;
+}
+
+export interface FlagEvaluationError extends Error {}
+
+/**
+ * Feature flags binding for evaluating feature flags from a Cloudflare Workers script.
+ *
+ * @example
+ * ```typescript
+ * // Get a boolean flag value with a default
+ * const enabled = await env.FLAGS.getBooleanValue('my-feature', false);
+ *
+ * // Get a flag value with evaluation context for targeting
+ * const variant = await env.FLAGS.getStringValue('experiment', 'control', {
+ *   userId: 'user-123',
+ *   country: 'US',
+ * });
+ *
+ * // Get full evaluation details including variant and reason
+ * const details = await env.FLAGS.getBooleanDetails('my-feature', false);
+ * console.log(details.variant, details.reason);
+ * ```
+ */
+export declare abstract class Flags {
+  /**
+   * Get a flag value without type checking.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Optional default value returned when evaluation fails.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  get(
+    flagKey: string,
+    defaultValue?: unknown,
+    context?: EvaluationContext
+  ): Promise<unknown>;
+
+  /**
+   * Get a boolean flag value.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getBooleanValue(
+    flagKey: string,
+    defaultValue: boolean,
+    context?: EvaluationContext
+  ): Promise<boolean>;
+
+  /**
+   * Get a string flag value.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getStringValue(
+    flagKey: string,
+    defaultValue: string,
+    context?: EvaluationContext
+  ): Promise<string>;
+
+  /**
+   * Get a number flag value.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getNumberValue(
+    flagKey: string,
+    defaultValue: number,
+    context?: EvaluationContext
+  ): Promise<number>;
+
+  /**
+   * Get an object flag value.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getObjectValue<T extends object>(
+    flagKey: string,
+    defaultValue: T,
+    context?: EvaluationContext
+  ): Promise<T>;
+
+  /**
+   * Get a boolean flag value with full evaluation details.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getBooleanDetails(
+    flagKey: string,
+    defaultValue: boolean,
+    context?: EvaluationContext
+  ): Promise<EvaluationDetails<boolean>>;
+
+  /**
+   * Get a string flag value with full evaluation details.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getStringDetails(
+    flagKey: string,
+    defaultValue: string,
+    context?: EvaluationContext
+  ): Promise<EvaluationDetails<string>>;
+
+  /**
+   * Get a number flag value with full evaluation details.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getNumberDetails(
+    flagKey: string,
+    defaultValue: number,
+    context?: EvaluationContext
+  ): Promise<EvaluationDetails<number>>;
+
+  /**
+   * Get an object flag value with full evaluation details.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getObjectDetails<T extends object>(
+    flagKey: string,
+    defaultValue: T,
+    context?: EvaluationContext
+  ): Promise<EvaluationDetails<T>>;
+}

types/generated-snapshot/experimental/index.d.ts

@@ -12733,6 +12733,140 @@ declare module "cloudflare:email" {
   };
   export { _EmailMessage as EmailMessage };
 }
+/**
+ * Evaluation context for targeting rules.
+ * Keys are attribute names (e.g. "userId", "country"), values are the attribute values.
+ */
+type EvaluationContext = Record<string, string | number | boolean>;
+interface EvaluationDetails<T> {
+  flagKey: string;
+  value: T;
+  variant?: string | undefined;
+  reason?: string | undefined;
+  errorCode?: string | undefined;
+  errorMessage?: string | undefined;
+}
+interface FlagEvaluationError extends Error {}
+/**
+ * Feature flags binding for evaluating feature flags from a Cloudflare Workers script.
+ *
+ * @example
+ * ```typescript
+ * // Get a boolean flag value with a default
+ * const enabled = await env.FLAGS.getBooleanValue('my-feature', false);
+ *
+ * // Get a flag value with evaluation context for targeting
+ * const variant = await env.FLAGS.getStringValue('experiment', 'control', {
+ *   userId: 'user-123',
+ *   country: 'US',
+ * });
+ *
+ * // Get full evaluation details including variant and reason
+ * const details = await env.FLAGS.getBooleanDetails('my-feature', false);
+ * console.log(details.variant, details.reason);
+ * ```
+ */
+declare abstract class Flags {
+  /**
+   * Get a flag value without type checking.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Optional default value returned when evaluation fails.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  get(
+    flagKey: string,
+    defaultValue?: unknown,
+    context?: EvaluationContext,
+  ): Promise<unknown>;
+  /**
+   * Get a boolean flag value.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getBooleanValue(
+    flagKey: string,
+    defaultValue: boolean,
+    context?: EvaluationContext,
+  ): Promise<boolean>;
+  /**
+   * Get a string flag value.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getStringValue(
+    flagKey: string,
+    defaultValue: string,
+    context?: EvaluationContext,
+  ): Promise<string>;
+  /**
+   * Get a number flag value.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getNumberValue(
+    flagKey: string,
+    defaultValue: number,
+    context?: EvaluationContext,
+  ): Promise<number>;
+  /**
+   * Get an object flag value.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getObjectValue<T extends object>(
+    flagKey: string,
+    defaultValue: T,
+    context?: EvaluationContext,
+  ): Promise<T>;
+  /**
+   * Get a boolean flag value with full evaluation details.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getBooleanDetails(
+    flagKey: string,
+    defaultValue: boolean,
+    context?: EvaluationContext,
+  ): Promise<EvaluationDetails<boolean>>;
+  /**
+   * Get a string flag value with full evaluation details.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getStringDetails(
+    flagKey: string,
+    defaultValue: string,
+    context?: EvaluationContext,
+  ): Promise<EvaluationDetails<string>>;
+  /**
+   * Get a number flag value with full evaluation details.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getNumberDetails(
+    flagKey: string,
+    defaultValue: number,
+    context?: EvaluationContext,
+  ): Promise<EvaluationDetails<number>>;
+  /**
+   * Get an object flag value with full evaluation details.
+   * @param flagKey The key of the flag to evaluate.
+   * @param defaultValue Default value returned when evaluation fails or the flag type does not match.
+   * @param context Optional evaluation context for targeting rules.
+   */
+  getObjectDetails<T extends object>(
+    flagKey: string,
+    defaultValue: T,
+    context?: EvaluationContext,
+  ): Promise<EvaluationDetails<T>>;
+}
 /**
  * Hello World binding to serve as an explanatory example. DO NOT USE
  */