Merge pull request #79 from sevenwestmedia-labs/feature/improve-client-typings

Feature: Improve client typings

Author: NathanP-7West

.changeset/loud-cheetahs-impress.md

@@ -0,0 +1,5 @@
+---
+'@etrigan/feature-toggles-client': minor
+---
+
+Improve typings via module augmentation.

package.json

@@ -43,5 +43,6 @@
         "eslint": "^7.12.1",
         "eslint-config-prettier": "^7.0.0",
         "eslint-config-wanews-base": "^2.2.0"
-    }
+    },
+    "packageManager": "yarn@1.22.22+sha512.a6b2f7906b721bba3d67d4aff083df04dad64c399707841b7acf00f6b133b7ac24255f2652fa22ae3534329dc6180534e98d17432037ff6fd140556e2bb3137e"
 }

packages/feature-toggles-client/src/index.ts

@@ -1,31 +1,36 @@
-export interface FeatureValue {
-    raw: any
+export interface FeatureValue<TValue = any> {
+    raw: TValue
     string(): string
     boolean(): boolean
 }
 
+/**
+ * Augment this interface at a global-level to improve the typing of returned features.
+ * https://www.typescriptlang.org/docs/handbook/declaration-merging.html#module-augmentation
+ */
 export interface RawFeatureValues {
     [feature: string]: unknown
 }
+
 /**
  * Current state of the feature toggles
  */
-export interface FeatureState {
-    [feature: string]:
+export type FeatureState = {
+    [key in keyof RawFeatureValues]?:
         | {
-              value: FeatureValue
+              value: FeatureValue<RawFeatureValues[key]>
 
               /** User overridable */
               canUserOverride: boolean
 
-              userOverride?: FeatureValue
+              userOverride?: FeatureValue<RawFeatureValues[key]>
           }
         | undefined
 }
 
-export function isFeatureEnabled<Features extends string>(
+export function isFeatureEnabled<TKey extends keyof RawFeatureValues>(
     toggles: FeatureState,
-    feature: Features,
+    feature: TKey,
     fallback = false,
 ): boolean {
     const featureState = toggles[feature]