store-project/src/reducers/cartReducer.js

export function cartReducer(state = {}, { type, good, count = 1 }) {
    if (count <= 0) {
        type = "CART_DELETE";
    }

    if (type === "CART_ADD") {
        return {
            ...state,
            [good["_id"]]: {
                good,
                count: good["_id"] in state ? state[good._id].count + count : count,
            },
        };
    }
    if (type === "CART_CHANGE") {
        return {
            ...state,
            [good["_id"]]: {
                good,
                count: count,
            },
        };
    }
    if (type === "CART_DELETE") {
        let { [good._id]: toRemove, ...newState } = state;
        return newState;
    }
    if (type === "CART_CLEAR") {
        return {};
    }
    return state;
}

export const actionCartAdd = (good, count = 1) => ({ type: "CART_ADD", good, count: +count });
export const actionCartChange = (good, count = 1) => ({ type: "CART_CHANGE", good, count: +count });
export const actionCartDelete = (good) => ({ type: "CART_DELETE", good });
export const actionCartClear = () => ({ type: "CART_CLEAR" });