from https://github.com/WordPress/packages/pull/106/files

packages/hooks/src/createHasHook.js

@@ -5,17 +5,24 @@
  * @param  {Object}   hooks Stored hooks, keyed by hook name.
  *
  * @return {Function}       Function that returns whether any handlers are
- *                          attached to a particular hook.
+ *                          attached to a particular hook and optional namespace.
  */
 function createHasHook( hooks ) {
 	/**
-	 * Returns how many handlers are attached for the given hook.
+	 * Returns whether any handlers are attached for the given hookName and optional namespace.
 	 *
-	 * @param  {string}  hookName The name of the hook to check for.
+	 * @param {string} hookName  The name of the hook to check for.
+	 * @param {string} namespace Optional. The unique namespace identifying the callback in the form `vendor/plugin/function`.
 	 *
 	 * @return {boolean} Whether there are handlers that are attached to the given hook.
 	 */
-	return function hasHook( hookName ) {
+	return function hasHook( hookName, namespace ) {
+		// Use the namespace if provided.
+		if ( 'undefined' !== typeof namespace ) {
+			return hookName in hooks &&
+				hooks[ hookName ].handlers.some( ( hook ) => hook.namespace === namespace );
+		}
+
 		return hookName in hooks;
 	};
 }

packages/hooks/src/test/index.test.js

@@ -697,3 +697,41 @@ test( 'removing a filter triggers a hookRemoved action passing all callback deta
 		'my_callback3'
 	);
 } );
+
+test( 'checking hasAction and hasFilter with named callbacks', () => {
+	// hasAction tests
+	addAction( 'test.action', 'my_callback', () => {} );
+	expect( hasAction( 'test.action', 'not_my_callback' ) ).toBe( false );
+	expect( hasAction( 'test.action', 'my_callback' ) ).toBe( true );
+
+	// test removing
+	removeAction( 'test.action', 'my_callback' );
+	expect( hasAction( 'test.action', 'my_callback' ) ).toBe( false );
+
+	// test removeAll
+	addAction( 'test.action', 'my_callback', () => {} );
+	addAction( 'test.action', 'my_second_callback', () => {} );
+	expect( hasAction( 'test.action', 'my_callback' ) ).toBe( true );
+	expect( hasAction( 'test.action', 'my_callback' ) ).toBe( true );
+	removeAllActions( 'test.action' );
+	expect( hasAction( 'test.action', 'my_callback' ) ).toBe( false );
+	expect( hasAction( 'test.action', 'my_callback' ) ).toBe( false );
+
+	// hasFilter tests
+	addFilter( 'test.filter', 'my_callback', () => {} );
+	expect( hasFilter( 'test.filter', 'not_my_callback' ) ).toBe( false );
+	expect( hasFilter( 'test.filter', 'my_callback' ) ).toBe( true );
+
+	// test removing
+	removeFilter( 'test.filter', 'my_callback' );
+	expect( hasFilter( 'test.filter', 'my_callback' ) ).toBe( false );
+
+	// test removeAll
+	addFilter( 'test.filter', 'my_callback', () => {} );
+	addFilter( 'test.filter', 'my_second_callback', () => {} );
+	expect( hasFilter( 'test.filter', 'my_callback' ) ).toBe( true );
+	expect( hasFilter( 'test.filter', 'my_second_callback' ) ).toBe( true );
+	removeAllFilters( 'test.filter' );
+	expect( hasFilter( 'test.filter', 'my_callback' ) ).toBe( false );
+	expect( hasFilter( 'test.filter', 'my_second_callback' ) ).toBe( false );
+} );