refactor: split StorageWrapper into sync and async interfaces for better type safety

Author: EmilianoSanchez

src/storages/inLocalStorage/__tests__/wrapper.mock.ts

@@ -4,7 +4,7 @@ import { loggerMock } from '../../../logger/__tests__/sdkLogger.mock';
 
 export const PREFIX = 'SPLITIO';
 
-export function createMemoryStorage(): SplitIO.StorageWrapper {
+export function createMemoryStorage(): SplitIO.AsyncStorageWrapper {
   let cache: Record<string, string> = {};
   return {
     getItem(key: string) {

src/storages/inLocalStorage/index.ts

@@ -19,7 +19,7 @@ import { ILogger } from '../../logger/types';
 import SplitIO from '../../../types/splitio';
 import { storageAdapter } from './storageAdapter';
 
-function validateStorage(log: ILogger, prefix: string, wrapper?: SplitIO.StorageWrapper): StorageAdapter | undefined {
+function validateStorage(log: ILogger, prefix: string, wrapper?: SplitIO.SyncStorageWrapper | SplitIO.AsyncStorageWrapper): StorageAdapter | undefined {
   if (wrapper) {
     if (isValidStorageWrapper(wrapper)) return storageAdapter(log, prefix, wrapper);
     log.warn(LOG_PREFIX + 'Invalid storage provided. Falling back to LocalStorage API');

src/storages/inLocalStorage/storageAdapter.ts

@@ -7,7 +7,7 @@ function isTillKey(key: string) {
   return key.endsWith('.till');
 }
 
-export function storageAdapter(log: ILogger, prefix: string, wrapper: SplitIO.StorageWrapper): Required<StorageAdapter> {
+export function storageAdapter(log: ILogger, prefix: string, wrapper: SplitIO.SyncStorageWrapper | SplitIO.AsyncStorageWrapper): Required<StorageAdapter> {
   let keys: string[] = [];
   let cache: Record<string, string> = {};
 

types/splitio.d.ts

@@ -458,19 +458,34 @@ interface IClientSideSyncSharedSettings extends IClientSideSharedSettings, ISync
  */
 declare namespace SplitIO {
 
-  interface StorageWrapper {
+  interface SyncStorageWrapper {
     /**
-     * Returns a promise that resolves to the current value associated with the given key, or null if the given key does not exist.
+     * Returns the value associated with the given key, or null if the key does not exist.
      */
-    getItem(key: string): Promise<string | null> | string | null;
+    getItem(key: string): string | null;
     /**
-     * Returns a promise that resolves when the value of the pair identified by key is set to value, creating a new key/value pair if none existed for key previously.
+     * Sets the value for the given key, creating a new key/value pair if key does not exist.
      */
-    setItem(key: string, value: string): Promise<void> | void;
+    setItem(key: string, value: string): void;
     /**
-     * Returns a promise that resolves when the key/value pair with the given key is removed, if a key/value pair with the given key exists.
+     * Removes the key/value pair for the given key, if the key exists.
      */
-    removeItem(key: string): Promise<void> | void;
+    removeItem(key: string): void;
+  }
+
+  interface AsyncStorageWrapper {
+    /**
+     * Returns a promise that resolves to the value associated with the given key, or null if the key does not exist.
+     */
+    getItem(key: string): Promise<string | null>;
+    /**
+     * Returns a promise that resolves when the value of the pair identified by key is set to value, creating a new key/value pair if key does not exist.
+     */
+    setItem(key: string, value: string): Promise<void>;
+    /**
+     * Returns a promise that resolves when the key/value pair for the given key is removed, if the key exists.
+     */
+    removeItem(key: string): Promise<void>;
   }
 
   /**
@@ -992,7 +1007,7 @@ declare namespace SplitIO {
      *
      * @defaultValue `window.localStorage`
      */
-    wrapper?: StorageWrapper;
+    wrapper?: SyncStorageWrapper | AsyncStorageWrapper;
   }
   /**
    * Storage for asynchronous (consumer) SDK.
@@ -1338,7 +1353,7 @@ declare namespace SplitIO {
        *
        * @defaultValue `window.localStorage`
        */
-      wrapper?: StorageWrapper;
+      wrapper?: SyncStorageWrapper | AsyncStorageWrapper;
     };
   }
   /**