has method for key presence check (#41)

* feat: Adding has method for key presence check

* feat: Adding has overload signature

* chore: Moving has method below get, adding api section for has

README.md

@@ -457,6 +457,8 @@ The injectable `ClsService` provides the following API to manipulate the cls con
     Set a value on the CLS context.
 -   **_`get`_**`(key?: string): any`  
     Retrieve a value from the CLS context by key. Get the whole store if key is omitted.
+-   **_`has`_**`(key: string): boolean`  
+    Check if a key is in the CLS context.
 -   **_`getId`_**`(): string;`  
     Retrieve the request ID (a shorthand for `cls.get(CLS_ID)`)
 -   **_`enter`_**`(): void;`  

src/lib/cls.service.spec.ts

@@ -93,6 +93,33 @@ describe('ClsService', () => {
         });
     });
 
+    describe('key presence', () => {
+        it('checks key presence (string key)', () => {
+            service.run(() => {
+                service.set('a', 1);
+                expect(service.has('a')).toEqual(true);
+            });
+        });
+        it('checks key absence (string key)', () => {
+            service.run(() => {
+                expect(service.has('b')).toEqual(false);
+            });
+        });
+        it('checks key presence (symbol key)', () => {
+            const sym = Symbol('sym');
+            service.run(() => {
+                service.set(sym, 123);
+                expect(service.has(sym)).toEqual(true);
+            });
+        });
+        it('checks key absence (symbol key)', () => {
+            const sym = Symbol('sym');
+            service.run(() => {
+                expect(service.has(sym)).toEqual(false);
+            });
+        });
+    });
+
     describe('edge cases', () => {
         it('returns undefined on nonexistent key', () => {
             service.run(() => {

src/lib/cls.service.ts

@@ -72,6 +72,22 @@ export class ClsService<S extends ClsStore = ClsStore> {
         return getValueFromPath(store as S, key as any) as any;
     }
 
+    /**
+     * Check if a key is in the CLS context
+     * @param key the key to check
+     * @returns true if the key is in the CLS context
+     */
+    has<T extends RecursiveKeyOf<S> = any>(
+        key: StringIfNever<T> | keyof ClsStore,
+    ): boolean;
+    has(key: string | symbol): boolean {
+        const store = this.namespace.getStore();
+        if (typeof key === 'symbol') {
+            return !!store[key];
+        }
+        return !!getValueFromPath(store as S, key as any);
+    }
+
     /**
      * Retrieve the request ID (a shorthand for `cls.get(CLS_ID)`)
      * @returns the request ID or undefined