Update item quantity if server result is different from client

assets/js/base/context/hooks/cart/use-store-cart-item-quantity.ts

@@ -66,6 +66,9 @@ export const useStoreCartItemQuantity = (
 		storeKey
 	);
 
+	// Update local state when server updates.
+	useEffect( () => setQuantity( cartItemQuantity ), [ cartItemQuantity ] );
+
 	// Track when things are already pending updates.
 	const isPending = useSelect(
 		( select ) => {

assets/js/blocks/cart-checkout/cart/test/block.js

@@ -178,4 +178,31 @@ describe( 'Testing cart', () => {
 		await waitFor( () => expect( fetchMock ).toHaveBeenCalled() );
 		expect( screen.getAllByRole( 'cell' )[ 1 ] ).toHaveTextContent( '16€' );
 	} );
+
+	it( 'updates quantity when changed in server', async () => {
+		const cart = {
+			...previewCart,
+			// Make it so there is only one item to simplify things.
+			items: [
+				{
+					...previewCart.items[ 0 ],
+					quantity: 5,
+				},
+			],
+		};
+		const itemName = cart.items[ 0 ].name;
+		render( <CartBlock /> );
+
+		await waitFor( () => expect( fetchMock ).toHaveBeenCalled() );
+		const quantityInput = screen.getByLabelText(
+			`Quantity of ${ itemName } in your cart.`
+		);
+		expect( quantityInput.value ).toBe( '2' );
+
+		act( () => {
+			dispatch( storeKey ).receiveCart( cart );
+		} );
+
+		expect( quantityInput.value ).toBe( '5' );
+	} );
 } );

assets/js/data/cart/actions.ts

@@ -393,11 +393,10 @@ export function* changeCartItemQuantity(
 	// eslint-disable-next-line @typescript-eslint/no-explicit-any -- unclear how to represent multiple different yields as type
 ): Generator< unknown, void, any > {
 	const cartItem = yield select( CART_STORE_KEY, 'getCartItem', cartItemKey );
-	yield itemIsPendingQuantity( cartItemKey );
-
 	if ( cartItem?.quantity === quantity ) {
 		return;
 	}
+	yield itemIsPendingQuantity( cartItemKey );
 	try {
 		const { response } = yield apiFetchWithHeaders( {
 			path: '/wc/store/cart/update-item',