Data: Fix issue with in-stack unsubscribe

data/index.js

@@ -28,7 +28,13 @@ let listeners = [];
  * Global listener called for each store's update.
  */
 export function globalListener() {
-	listeners.forEach( listener => listener() );
+	// Use for loop instead of Array#forEach, as it's possible a listener's
+	// behavior causes one further in the stack to be unsubscribed. The
+	// latter's callback should not be called, which requires monitoring
+	// changes to the array as they occur in iteration.
+	for ( let i = 0; i < listeners.length; i++ ) {
+		listeners[ i ]();
+	}
 }
 
 /**

data/test/index.js

@@ -209,6 +209,20 @@ describe( 'withDispatch', () => {
 } );
 
 describe( 'subscribe', () => {
+	const unsubscribes = [];
+	afterEach( () => {
+		let unsubscribe;
+		while ( ( unsubscribe = unsubscribes.shift() ) ) {
+			unsubscribe();
+		}
+	} );
+
+	function subscribeWithUnsubscribe( ...args ) {
+		const unsubscribe = subscribe( ...args );
+		unsubscribes.push( unsubscribe );
+		return unsubscribe;
+	}
+
 	it( 'registers multiple selectors to the public API', () => {
 		let incrementedValue = null;
 		const store = registerReducer( 'myAwesomeReducer', ( state = 0 ) => state + 1 );
@@ -233,6 +247,21 @@ describe( 'subscribe', () => {
 
 		expect( incrementedValue ).toBe( 3 );
 	} );
+
+	it( 'avoids calling a later listener if unsubscribed during earlier callback', () => {
+		const store = registerReducer( 'myAwesomeReducer', ( state = 0 ) => state + 1 );
+		const firstListener = jest.fn( () => {
+			secondUnsubscribe();
+		} );
+		const secondListener = jest.fn();
+
+		subscribeWithUnsubscribe( firstListener );
+		const secondUnsubscribe = subscribeWithUnsubscribe( secondListener );
+
+		store.dispatch( { type: 'dummy' } );
+
+		expect( secondListener ).not.toHaveBeenCalled();
+	} );
 } );
 
 describe( 'dispatch', () => {