Javascript 更改数组逻辑内 object 内的属性

Question

        case ActionTypes.ADD_TO_CART: {
        var newOrders = state.cartItems.slice();
        let updatedIem = state.cartItems.find(i => {
            if (i.id === action.product.id) {
                return action.product
            }
            else {
                return null
            }
        });
        if (updatedIem) {
            var oldOrder = newOrders[action.itemIndex];
            var newOrder = Object.assign({}, oldOrder);
            if (action.direction == 1 && newOrder.quantity > 0) {
                newOrder.qty++;
                newOrder.quantity--;
            }
            else if (action.direction == -1 && newOrder.qty != 0 && newOrder.quantity > 0) {
                newOrder.qty--;
                newOrder.quantity++;
            }
            else null

            newOrders[action.itemIndex] = newOrder;
        }
        else {
            newOrders[action.itemIndex] = action.product
        }
        return {
            ...state,
            cartItems: newOrders,
        };
    }

This code returns an Array cartItems in the returned object but the problem is that one of Array elements is undefined , as in: [{first object}, undefined, {third object}] .

The undefined element is not wanted. I know it's coming from one of the assignments to newOrders[action.itemIndex] but I don't know how to track this down.

Answer 1

I see two ways to approach this problem:

(1) Make sure that you are not inserting undefined objects into your array. You can do this with a simple (object == null) check. This will capture null and undefined objects.

(2) Filter out undefined objects, eg cartArray = cartArray.filter(item => item != null) .