feat(toolkit/storage): allow synchronous retrieval of an item

```ts
   const storage = new WebStorage(window.sessionStorage);
   const item = storage.get('key');
```

projects/scion/toolkit/storage/src/web-storage.spec.ts

@@ -201,32 +201,89 @@ describe('WebStorage', () => {
     });
   });
 
+  describe('WebStorage.get', () => {
+
+    it('should return the value associated with the given key', () => {
+      const testee = new WebStorage(window.sessionStorage);
+      testee.put('key', 'value');
+      expect(testee.get('key')).toEqual('value');
+    });
+
+    it('should return the object associated with the given key', () => {
+      const testee = new WebStorage(window.sessionStorage);
+      const value = {p1: 'value', p2: 2, p3: true};
+      testee.put('key', value);
+      expect(testee.get('key')).toEqual(value);
+    });
+
+    it('should return `undefined` if no item is associated with the given key', () => {
+      const testee = new WebStorage(window.sessionStorage);
+      expect(testee.get('key')).toBeUndefined();
+    });
+
+    it('should return `null` if the `null` value is associated with the given key', () => {
+      const testee = new WebStorage(window.sessionStorage);
+      testee.put('key', null);
+      expect(testee.get('key')).toBeNull();
+    });
+
+    it('should return `undefined` if the `undefined` value is associated with the given key', () => {
+      const testee = new WebStorage(window.sessionStorage);
+      testee.put('key', undefined);
+      expect(testee.get('key')).toBeUndefined();
+    });
+
+    it('should return `0` if the `0` value is associated with the given key (falsy value)', () => {
+      const testee = new WebStorage(window.sessionStorage);
+      testee.put('key', 0);
+      expect(testee.get('key')).toEqual(0);
+    });
+
+    it('should return `false` if the `false` value is associated with the given key (falsy value)', () => {
+      const testee = new WebStorage(window.sessionStorage);
+      testee.put('key', false);
+      expect(testee.get('key')).toBeFalse();
+    });
+
+    it('should return an empty string if the "" value is associated with the given key (falsy value)', () => {
+      const testee = new WebStorage(window.sessionStorage);
+      testee.put('key', '');
+      expect(testee.get('key')).toEqual('');
+    });
+
+    it('should throw if failed to parse the value associated with the given key', () => {
+      const testee = new WebStorage(window.sessionStorage);
+      sessionStorage.setItem('key', 'VALUE NOT IN JSON FORMAT');
+      expect(() => testee.get('key')).toThrowError(/Unexpected token V in JSON/);
+    });
+  });
+
   describe('WebStorage.isPresent', () => {
 
-    it('should not be present if no value is associated with the key', async () => {
+    it('should not be present if no value is associated with the key', () => {
       const testee = new WebStorage(window.sessionStorage);
       expect(testee.isPresent('key')).toBeFalse();
     });
 
-    it('should be present if the `null` value is associated with the key', async () => {
+    it('should be present if the `null` value is associated with the key', () => {
       const testee = new WebStorage(window.sessionStorage);
       sessionStorage.setItem('key', null);
       expect(testee.isPresent('key')).toBeTrue();
     });
 
-    it('should be present if the `undefined` value is associated with the key', async () => {
+    it('should be present if the `undefined` value is associated with the key', () => {
       const testee = new WebStorage(window.sessionStorage);
       sessionStorage.setItem('key', undefined);
       expect(testee.isPresent('key')).toBeTrue();
     });
 
-    it('should be present if a value is associated with the key', async () => {
+    it('should be present if a value is associated with the key', () => {
       const testee = new WebStorage(window.sessionStorage);
       sessionStorage.setItem('key', 'value');
       expect(testee.isPresent('key')).toBeTrue();
     });
 
-    it('should be present if a falsy value is associated with the key', async () => {
+    it('should be present if a falsy value is associated with the key', () => {
       const testee = new WebStorage(window.sessionStorage);
       testee.put('key', 0);
       expect(testee.isPresent('key')).toBeTrue();

projects/scion/toolkit/storage/src/web-storage.ts

@@ -10,7 +10,6 @@
 
 import {EMPTY, fromEvent, merge, Observable, Observer, of, Subject, TeardownLogic} from 'rxjs';
 import {distinctUntilChanged, filter, mapTo, mergeMap, startWith, takeUntil} from 'rxjs/operators';
-import {Defined} from '@scion/toolkit/util';
 
 /**
  * Allows observing items contained in web storage (local storage or session storage).
@@ -61,6 +60,32 @@ export class WebStorage {
     }
   }
 
+  /**
+   * Returns the item associated with the given key, or `undefined` if not found.
+   *
+   * Expects the value to be stored in JSON format. Throws an error if the value cannot be parsed.
+   */
+  public get<T>(key: string): T | null | undefined {
+    const item = this._storage.getItem(key);
+
+    // Web storage returns `null` if there is no item associated with the key.
+    if (item === null) {
+      return undefined;
+    }
+
+    // If the value `undefined` is associated with the key, web storage returns 'undefined' as string.
+    if (item === 'undefined') {
+      return undefined;
+    }
+
+    // If the value `null` is associated with the key, web storage returns 'null' as string.
+    if (item === 'null') {
+      return null;
+    }
+
+    return JSON.parse(item);
+  }
+
   /**
    * Removes the item associated with the given key.
    */
@@ -88,6 +113,7 @@ export class WebStorage {
    * with the given key upon subscription. By default, `emitIfAbsent` is set to `false`.
    */
   public observe$<T>(key: string, options?: {emitIfAbsent?: boolean}): Observable<T> {
+    const emitIfAbsent = options?.emitIfAbsent ?? false;
     const otherDocumentChange$ = fromEvent<StorageEvent>(window, 'storage')
       .pipe(
         filter(event => event.storageArea === this._storage),
@@ -102,32 +128,18 @@ export class WebStorage {
           filter(itemKey => itemKey === key),
           startWith(key),
           mergeMap(itemKey => {
-              const item = this._storage.getItem(itemKey);
-
-              // Web storage returns `null` if there is no item associated with the key.
-              if (item === null) {
-                return Defined.orElse(options?.emitIfAbsent, false) ? of(undefined) : EMPTY;
-              }
-
-              // If the value `undefined` is associated with the key, web storage returns 'undefined' as string.
-              if (item === 'undefined') {
-                return of(undefined);
-              }
-
-              // If the value `null` is associated with the key, web storage returns 'null' as string.
-              if (item === 'null') {
-                return of(null);
-              }
-
-              try {
-                return of(JSON.parse(item));
-              }
-              catch (error) {
-                console.warn(`Failed to parse item from storage. Invalid JSON. [item=${item}]`, error);
-                return EMPTY;
-              }
-            },
-          ),
+            if (!this.isPresent(itemKey)) {
+              return emitIfAbsent ? of(undefined) : EMPTY;
+            }
+
+            try {
+              return of(this.get<any>(itemKey));
+            }
+            catch (error) {
+              console.warn(`Failed to parse item from storage. Invalid JSON. [key=${itemKey}]`, error);
+              return EMPTY;
+            }
+          }),
           distinctUntilChanged(),
           takeUntil(unsubscribe$),
         )