Feature/custom types

README.md

@@ -224,6 +224,28 @@ const unleashContext = {
 unleash.isEnabled('someToggle', unleashContext);
 ```
 
+## TypeScript: Custom Feature Toggle Names
+
+You can use TypeScript module augmentation to provide type safety for your feature toggle names.
+This ensures that only specific feature names can be used with `isEnabled` and related methods,
+catching typos at compile time.
+
+```typescript
+import { initialize } from 'unleash-client';
+
+declare module 'unleash-client' {
+  interface CustomTypeOptions {
+    name: 'aaa' | 'bbb';
+  }
+}
+
+const client = initialize({});
+
+client.isEnabled('aaa');
+client.isEnabled('bbb');
+client.isEnabled('ccc'); // Error
+```
+
 ## Advanced usage
 
 The initialize method takes the following arguments:

src/client.ts

@@ -17,6 +17,23 @@ interface BooleanMap {
   [key: string]: boolean;
 }
 
+/**
+ * Type for toggle name queries. Defaults to string but can be augmented by users.
+ * Users can extend this via module augmentation:
+ *
+ * declare module 'unleash-client' {
+ *   interface CustomTypeOptions {
+ *     name: string;
+ *   }
+ * }
+ */
+export interface CustomTypeOptions {}
+
+type GetCustom<K extends PropertyKey, Fallback> = K extends keyof CustomTypeOptions
+  ? CustomTypeOptions[K]
+  : Fallback;
+export type Name = GetCustom<'name', string>;
+
 export default class UnleashClient extends EventEmitter {
   private repository: RepositoryInterface;
 
@@ -106,7 +123,7 @@ export default class UnleashClient extends EventEmitter {
     });
   }
 
-  isEnabled(name: string, context: Context, fallback: Function): boolean {
+  isEnabled(name: Name, context: Context, fallback: Function): boolean {
     const feature = this.repository.getToggle(name);
     const enabled = this.isFeatureEnabled(feature, context, fallback).enabled;
 

src/index.ts

@@ -7,12 +7,14 @@ import { UnleashEvents } from './events';
 import { ClientFeaturesResponse } from './feature';
 import InMemStorageProvider from './repository/storage-provider-in-mem';
 import { UnleashConfig } from './unleash-config';
+import { CustomTypeOptions, Name } from './client';
 
 // exports
 export { Strategy } from './strategy/index';
 export { Context, Variant, PayloadType, Unleash, TagFilter, InMemStorageProvider, UnleashEvents };
 export type { ClientFeaturesResponse, UnleashConfig };
 export { UnleashMetricClient } from './impact-metrics/metric-client';
+export { CustomTypeOptions, Name };
 
 let instance: undefined | Unleash;
 
@@ -30,7 +32,7 @@ export async function startUnleash(options: UnleashConfig): Promise<Unleash> {
   return unleash;
 }
 
-export function isEnabled(name: string, context: Context = {}, fallbackValue?: boolean): boolean {
+export function isEnabled(name: Name, context: Context = {}, fallbackValue?: boolean): boolean {
   return instance ? instance.isEnabled(name, context, fallbackValue) : !!fallbackValue;
 }
 

src/unleash.ts

@@ -1,6 +1,6 @@
 import { tmpdir } from 'os';
 import { EventEmitter } from 'events';
-import Client from './client';
+import Client, { Name } from './client';
 import Repository, { RepositoryInterface } from './repository';
 import Metrics from './metrics';
 import { Context } from './context';
@@ -270,9 +270,9 @@ export class Unleash extends EventEmitter {
     Unleash.instanceCount--;
   }
 
-  isEnabled(name: string, context?: Context, fallbackFunction?: FallbackFunction): boolean;
-  isEnabled(name: string, context?: Context, fallbackValue?: boolean): boolean;
-  isEnabled(name: string, context: Context = {}, fallback?: FallbackFunction | boolean): boolean {
+  isEnabled(name: Name, context?: Context, fallbackFunction?: FallbackFunction): boolean;
+  isEnabled(name: Name, context?: Context, fallbackValue?: boolean): boolean;
+  isEnabled(name: Name, context: Context = {}, fallback?: FallbackFunction | boolean): boolean {
     const enhancedContext = { ...this.staticContext, ...context };
     const fallbackFunc = createFallbackFunction(name, enhancedContext, fallback);