example.js

    [cartActions.INCREMENT_CART_ITEM_QTY]({ commit, state }, cartItemId) {
        let clonedCartItems = {...state.cartItems}
        clonedCartItems[cartItemId].qty++
        let actualCartItems = []
        for (let key in clonedCartItems) {
            let currentCartItem = clonedCartItems[key]
            actualCartItems.push({
                id: currentCartItem.id,
                product_id: currentCartItem.product_id,
                qty: currentCartItem.qty
            })
        }

        CartService.updateCartState(state.cartId, actualCartItems)
            .then(data => {
                let cartDetails = data.result
                commit(cartMutations.SET_CART_DETAILS, cartDetails)
            })
    },