React-busser NPM

busser

A robust, opinionated, UI state flow management option for scalable and precise communication across ReactJS Components rendered on either the client-side or server-side. It heavily compliments react-query (@tanstack/react-query). busser is a synchronous state manager while react-query (@tanstack/react-query) is an asynchronous state manager. Just the same way RTK and RTK Query handle UI state and Server state respectively, busser and react-query (@tanstack/react-query) handle UI state and Server state respectively.

Preamble

This library is made up of custom ReactJS hooks that provide basic tools to build stateful web applications that scale well even as the size of UI state and data flow paths grow or ranch out in very undeterministic manners. It makes it very easy to manage not just UI state but data flow across each React components that needs to access, share or recompute state in an effiecient manner. busser achieves this by using an event bus, eliminating wasteful re-renders where necessary by employing signals and utilizing the best places to store specific kinds of UI state.

There are 2 broad categories into which we can classify all of the state that any ReactJS app deals with

Transient or Temporary state (e.g. UI state, derived state)
Non-Transient or Permanent state (e.g. Server state, base state)

------------------------------------------------------

Hooks that manage state in Storage

useBrowserStorage()
useBrowserStorageWithEncryption()

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Hooks that manage the flow of state in Storage

useBrowserStorageEvent()

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Hooks that manage state in Memory

useList()
useComposite()
useCount()
useProperty()
usePromised()
useSignalsList()
useSignalsComposite()
useSignalsCount()
useSignalsProperty()

Hooks that manage flow of state in Memory

useBus()
useOn()
useSharedState()

------------------------------------------------------

Hooks specialized for specific tasks

useControlKeysPress()
useTextFilteredList()
useTextFilteredSignalsList()
useUICommands()

It's very important to note that busser exists only because of the inefficiencies present in the implementation of ReactJS. ReactJS claims to be wholly reactive but it really isn't because ReactJS is by definition a tree of interactive components, imperatively controlling and communicating with one another. This creates the restriction (i was speaking about earlier) for the pathways that data can travel in the web application. Libraries like MobX, pursue the wholly reactive option using Observables. However, busser borrows from MobX but unlike MobX, busser makes the component wholly reactive from the inside rather than from the outside.

Motivation

The philosophy of ReactJS can be summarized using 2 phrases: uni-directional data flow and view-model state reconciliation. This philosophy is great for the most part (as it promotes things like the locality of behavior) until you need to have fine-grained state updates (not to be confused with fine-grained reactivity). ReactJS doesn't utilize reactivity at any level - This is because that goes against the "re-render everything with idempotence" mantra. ReactJS strongly suggests that side effects be hidden inside useEffect() and only deal with React-y stuff inside components and hooks but it's not always that simple. Firstly, useEffect() dependency list doesn't play nice with reference types (object, object literals and arrays). Secondly, useMemo() and useCallback() don't offer memoization in the true sense of the word - they only offer memoization between one render and the very next render following in turn. Finally, it's not every time you want a state change to trigger a re-render (especially of an entire sub-tree). Also, it's also not every time you need user interaction(s) on the UI to lead to a state change that eventually updates the UI (after consulting the VDOM). These cases are not catered for completely by ReactJS out-of-the-box. Though, the React core team has made some effort to cater to these issues over time but it hasn't been comprehensive. Even until recently, with the promotion of React Forget, ReactJS still struggles with providing a more comprehensive solution to the re-render problem.

Furthermore, there's an increase in the use of React Context in building our react apps because of it many benefits. However, React context has it's own drawbacks too and also it's painful performance issues at scale. Also, over-using props to pass data around and/or trigger state changes can slow React down significantly especially at scale. You might say: "So ? that's exactly why React context was created - to help avoid prop drilling" and you'd be partly right but (as stated earlier) using useContext() excessively can also lead to wasteful re-renders. Sure, this "wasteful re-renders" issue can be solved with libraries like use-context-selector but again at a very high cost and has some limitations. The deeper a component using useContext() is in the component-tree hierarchy of a ReactJS app combined with more frequent UI state changes, the slower at rendering (and re-rendering) the app becomes even without props. All these issues are negligible with small ReactJS app with little client-side interactivity. However, they become more pronounced over time in large ReactJS apps that have a much larger scale of client-side interactivity.

Busser seeks to reduce and/or eliminate these issues as much as is possible so you don't have to think too much about things that don't make you more productive at resolving bugs or building out features. Busser proposes a new way. This way involves reducing the number of props used by components to pass/transfer data by utilising events instead. This way/method is known as "pruning the leaves". What this way/method of setting up data transfer amongst React components tries to achieve is to "prune the leaves" of the component tree and make fine-graned state updates easy and possible. The prolific teacher of ReactJS (@kentcdodds), wrote something resembling this idea of "pruning leaves" the component tree here: https://epicreact.dev/one-react-mistake-thats-slowing-you-down. This makes the entire component tree faster at re-rending by making the children of erstwhile parent components to be siblings.

Therefore, this package (busser) seeks to promote the idea that communication between React components should not be limited to props/context or through parent components alone. It utilizes the Mediator Coding Pattern (event bus model) to allow components communicate in a more constrained yet scalable way. This package was inspired partially by react-bus, redux and jotai. This package can also be used well with react-query (@tanstack/react-query) to create logic that can work hand-in-hand to promote less boilerplate for repititive react logic (e.g. data fetching + management) and promote cleaner code.

Why is it necessary to adopt this novel way with Busser ?

There are 2 major reasons why it's important to "prune the leaves" of React component tree for your app as seen below:

The virtual DOM is vital to how React works but also presents challenges of it's own in the manner in which it works. Some of these challenges include updating leave DOM nodes too often and not optimizing DOM updates where text node values are unchanged. The idea here is to try to workaround these challenges by trying to minimize the amount of wasteful re-renders the virtual DOM is bound to honour so that:

1. The tree diff algorithm keeps on updating leaf (and parent) nodes that do not need to be updated: The premise for this is that the time complexity of the tree diff algorithm used in ReactJS is linear time (O(n)) and doesn't just swap values (e.g. DOM attributes, DOM text nodes) in place (the way signals do) from the virtual DOM to the real DOM. It actually replaces it in a top-down replacement approach, the entire sub-tree and not just the node that changed. Therefore, you might end up with bugs like this one sometimes.
1. The CPU computation cost due to the tree diff algorithm used in updating/commiting into the DOM is heavy: The premise here is that computing the difference between the real DOM and virtual is usually expensive when the scale of client interactivity is high.

The amount of wasteful re-renders are intensified without much effort in an almost exponential manner as the component tree grows deeper and widder/larger. In fact, when it comes to rendering thing like lists or modals, it is imperetive (as far as React is concerned) that extra steps be taken by the developer to aid the heuristics/assumptions used by the Virtual DOM in reconciling the DOM cheaply. React, by default, cannot perform optimizations without these extra steps.

1. Memo ReactJS APIs aren't always reliable when setup: One could utilize the useMemo() and useCallback() (like the now decommisioned: useEvent() hook) functions to greatly reduce the number of wasteful re-renders. However, sometimes, tools like useMemo() and useCallback() don't always work well to reduce wasteful re-renders (especially when the dependency array passed to them contains values that change very frequently or contain reference types that are re-created on every render). Now, with the coming of ReactJS 19 and its' big set of changes, some of these memo APIs will be retired in favour of a compiler.

Busser: the novel way

It's important to note that busser can be used in one or all of 3 scenarios:

Sharing global base/derived state across multiple ReactJS components.
Sharing local base state across multiple ReactJS components.
Sharing local derived state across multiple ReactJS components.

Global state is managed by the useSharedState() hook (or the useSharedSignalsState() - if you prefer to use signals) which should only be used when state needs to be accessed/shared and updated by multiple client-side components.

There are a couple of rules that should be top of mind when using busser in any of these scenarios for maximum benefit. They are as follows:

Do not grow the component tree depth-wise, it's better to grow it breadth-wise instead (whenever you can) to cut down the use of props drastically (especially props that change often - transient state / UI state).
Endeavour to pass mostly non-transient data via props to presentation/leaf components and seldom to container components. If it is ever a must to pass transient data via props, let it be at the top of the component-tree hierarchy of the ReactJS app.
All props should only be delivered from exactly one parent component to exactly one child component at any time (but there can be exceptions).
Make use of key prop when rendering ReactJS components whether in a loop or not. This can help the Virtual DOM with ae-arranging and re-rendering in a cheaper way.

Old Concepts, New Setup

At the core, busser is simply a collection of ReactJS hooks. The concept of an event bus (implemented using the Mediator Coding Pattern or Pub/Sub) employed to pass data around in parts of a frontend (and backend) software applications isn't new. This (pub/sub - think Redis) concept has been around for a long time in software developement and while being very vital to service-oriented/kernel software architecture and systems, it has been plagued in its use at scale when deployed on frontend web applications by lacking a set of correct and adequate logic constraints at scale as well as debug data about the events being fired in an orderly (and not a hapharzard) manner. It's very easy to overuse and by consequence get overwhelmed by the sheer number and frequency of events (from event buses) and data being fired and passed around respectively. However, the biggest issue with this concept at scale is managing the predicatability and flow of these events. So, this project proposed 1 specific way to communicate across components (as broadcasts - i.e. events fired from source to destination):

cascade broadcasts

Therefore, the philosophy upon which react-busser operates and works is as follows:

An evented object (event bus) system built on ReactJS hooks.
Builds upon the existing state management features (useState(), useRef(), useCallback(), useContext()) already provided by ReactJS.
Emphazises and encourages prudent use of ReactJS props as well as the creation of child components only when necessary. The creation of sibling components is more prefered (remember as earlier said 👆🏾 - "prunning the leaves") to the creation of more child components.
Makes ReactJS component and business logic (in ReactJS hooks) more readable, reusable and maintainable by decoupling and relegating such logic to the ReactJS component that truly OWNS the logic (and not ancestor/parent components).

Take a look at examples of custom ReactJS hooks built with react-busser:

Let's create a hook for knowing when a page element is scrolled vertically

import { useEffect, MutableRefObject, ComponentProps } from 'react';
import { useBus } from 'react-busser';

export const useVerticallyScrolled = (
  { threshold = 100 }: { threshold: number },
  ref: MutableRefObject<HTMLElement>
) => {
  const [ bus ] = useBus(
    { subscribes: [], fires: ["document:vertical:scrolled"] },
    "App.document"
  );

  useEffect(() => {
    const target = ref && ref.current.nodeName !== "HTML" ? ref.current : window;
    const handleScroll = () => {
      let value = -1;
      let boxGap = target.offsetHeight - target.clientHeight;
      let offset = target.pageYOffset || (target.scrollHeight - target.clientHeight - boxGap) || target.scrollTop;

      if (offset <= threshold) {
        value = offset;
      } else {
        value = threshold;
      }

      bus.emit("document:vertical:scrolled", value);
    };
    target.addEventListener("scroll", handleScroll);

    return () => {
      target.removeEventListener("scroll", handleScroll);
    };
  /* eslint-disable-next-line react-hooks/exhaustive-deps */
  }, [threshold, ref]);
}

// useVerticallyScrolled({ threshold: 450 });

Let's create a set of hooks for powering modals

Step 1: create a modal UI component

import React from "react";
import ReactDOM from "react-dom";

type CustomElementTagProps<T extends React.ElementType> = React.ComponentPropsWithRef<T> & {
  as?: T;
}

const Modal = React.forwardRef<
  HTMLDivElement,
  React.HTMLAttributes<HTMLDivElement> & { wrapperClassName?: string, close: (() => void) }
>(function Modal (props, ref) {
  const { id, wrapperClassName = "", className = "", ...nodeProps } = props;

  const hasChildren = (children: React.ReactNode, count: number) => {
    const childCount = React.Children.count(children);
    return childCount === count;
  };

  const isSubChild = (child: React.ReactNode, tag: string) =>
    React.isValidElement(child) && String(child?.type).includes(tag);

  const renderChildren = (chidren: React.ReactNode, { close, parent = "Modal" }) => {
    const oneChild = hasChildren(children, 1);
    const topChildren = React.Children.toArray(children);

    if (parent === "Modal") {
      const [ parentChild ] = topChildren;
      if (!oneChild || parentChild.type === React.Fragment) {
        console.error(
          "[Error]: valid Modal inner wrapper component not found"
        )
        return null;
      }
    }

    

    if (typeof children === "object") {
      if (children !== null && children !== undefined) {

        if (parent === "Modal") {
          const [ parentChild ] = topChildren;
          if (!("props" in parentChild)
            || (typeof parentChild.props.children !== "object" && parentChild.props.children !== null)
              || React.Children.count(parentChild.props.children) !== 3) {
            console.error(
              "[Error]: Modal must have at least 3 valid children; <Modal.Header />, <Modal.Body /> and <Modal.Footer />"
            );
            return null;
          }

          return topChildren.map((child) => {
            if (!React.isValidElement(child)) {
              return null;
            }

            const { children, ...childProps } = child.props;
            return (
              <child.type {...childProps}>
                {
                  React.Children.map(child.props.children, (innerChild) => {
                    switch (true) {
                      case parent === "Modal" && isSubChild(child, "Header"):
                      case parent === "Modal" && isSubChild(child, "Footer"):
                      case parent === "Modal" && isSubChild(child, "Body"):
                        return React.cloneElement(
                          child,
                          {
                            close: close
                          }
                        )
                        break;
                      default:
                        return null
                        break;
                    }
                  })
                }
              </child.type>
            );
          });
        }

        return React.Children.map(children, ($child) => {
          switch (true) {
            case parent !== "Modal" && React.isValidElement($child):
              return React.cloneElement(
                $child,
                {
                  close: close
                }
              )
              break;
            default:
              return null
              break;
          }
        })
      }
    }

    return null;
  };

  return (
    ReactDOM.createPortal(
      <div className={className || ""} id={id} ref={ref}>
        <div className={wrapperClassName || ""}>
          {
            renderChildren(
              nodeProps.children,
              { close: nodeProps.close }
            )
          }
        </div>
      </div>,
      document.body
    );
  );
});

const Header = (
  {
    as: Component = "div",
    close,
    className,
    ...props
  }: {
    className?: string;
    close?: () => void;
    children?: React.ReactNode;
    as: React.ElementType
  }) => {
  return (
    <Component className={className}>
      {renderChildren(
        children,
        { close, parent: "Header" }
      )}
    </Component>
  );
};

type BodyProps = ComponentProps<"section"> & { close?: () => void };

const Body = (
  {
    children,
    close,
    className
  }: BodyProps) => {
  return (
    <section className={className}>
      {renderChildren(
        children,
        { close, parent: "Body" }
      )}
    </section>
  );
};

const Footer = ({
  as: Component = "div",
  close,
  className,
  children
}: {
  close?: () => void;
  className?: string;
  children?: React.ReactNode;
  as: React.ElementType
}) => {
  return (
    <Component className={className}>
      {renderChildren(
        children,
        { close, parent: "Footer" }
      )}
    </Component>
  );
};

Modal.Header = Header;
Modal.Body = Body;
Modal.Footer = Footer;

type HeaderProps = ComponentProps<typeof Header>;
type FooterProps = ComponentProps<typeof Footer>;

export { 
  HeaderProps,
  BodyProps,
  FooterProps
}

export default Modal;

Step 2: create 2 hooks to manage showing and hiding the modals

import React, { useState, useMemo, useRef, useEffect } from 'react';
import { useOutsideClicked, useSearchParamsState } from 'react-busser';

import Modal from './Modal';

export function useModalCore (styles: {
  className: string, wrapperClassName: string
}) {
  const sequentialIdGeneratorFactory = (): (() => string) => {
    let i = 0;
    return () => `$__modal_${i++}`;
  };
  const markModalsPosition = useRef<Record<string, { position: number, ref: React.MutableRefObject }>>({});
  const [modals, setModals] = useState<React.ReactElement[]>([]);
  const controls = useMemo(
    () => {

      const idGeneratorRoutine: string = sequentialIdGeneratorFactory();
      const close = (modalRefId: string, callback: (() => void)) => {

          let id = modalRefId;

          setModals((prevModals) => {
            if (!id) {
              return prevModals;
            }

            const clonedPrevModals = prevModals.slice(0);
            const { position, ref } = markModalsPosition.current[id];

            clonedPrevModals.splice(position, 1);
            delete markModalsPosition.current[id];

            ref.current = null;

            return clonedPrevModals;
          });
          callback()
      };

      return {
        show (node: React.ReactNode, reference: React.MutableRefObject, callback: (() => void)) {
          if (reference.current !== null) {
            return reference.current.id;
          }

          const id = idGeneratorRoutine();
          /* @CHECK: https://legacy.reactjs.org/docs/reconciliation.html#tradeoffs */
          const modal = <Modal key={id} className={styles.className} wrapperClassName={styles.wrapperClassName} id={id} close={close.bind(null, id, callback)} ref={reference}>{node}</Modal>;

          setModals((prevModals) => {
            markModalsPosition.current[id] = { position: prevModals.length, ref: reference };
            return [...prevModals, modal];
          });

          return id;
        },
        close: close
      }
    },
    []
  );

  useEffect(() => {
   return () => {
     markModalsPosition.current = {}
     setModals([]);
   };
  /* eslint-disable-next-line react-hooks/exhaustive-deps */
  }, []);

  return [modals, controls];
}

export const useModalControls = (
  controls: { show: (node: React.ReactNode) => string, close: (modalId: string) => void },
  id: string
) => {
  const modalNode = useRef<React.ReactNode | null>(null);
  const [ modalVisibilityState, setModalVisibilityState, unsetParamsOnUrl ] = useSearchParamsState<"hidden" | "visible">(
    id,
    false,
    "hidden"
  );
  const [ modalRef ] = useOutsideClick((subject) => {
    setModalVisibilityState((prevModalVisibilityState) => {
      if (prevModalVisibilityState === "visible") {
        return "hidden";
      }
      return prevModalVisibilityState;
    });
    /* @NOTE: Close the modal if any DOM element outside it is clicked */
    controls.close(subject.id);
  });

  const hasNoChild = (children: React.ReactNode) => {
    const childCount = React.Children.count(children);
    const hasZeroChild = childCount === 0;
    return hasZeroChild;
  };

  useEffect(() => {
    return () => {
      modalNode.current = null;
      unsetParamsOnUrl();
    }
  /* eslint-disable-next-line react-hooks/exhaustive-deps */
  }, []);

  if (modalVisibilityState === "visible") {
    if (modalNode.current !== null) {
      if (modalRef.current === null) {
        /* @HINT: Automatically show the modal when page is freshly loaded 
            with <URL> + query params containing `modalVisibilityState`
        */
        controls.show(
          React.cloneElement(
            modalNode.current,
            { id }
          ),
          modalRef,
          () => setModalVisibilityState(
            (prevModalVisibilityState) => {
              if (prevModalVisibilityState === "visible") {
                return "hidden";
              }
              return prevModalVisibilityState;
            }
          )
        );
      }
    }
  } else {
    if (modalRef.current !== null) {
      setModalVisibilityState("hidden")
      controls.close(subject.id);
    }
  }

  return {
    get isModalVisible () {
      return modalVisibilityState === "visible";
    },
    showModal (node: React.ReactNode) {
      if (hasNoChild(node)) {
        throw new Error("cannot display this modal!");
      }
      
      if (modalRef.current !== null && modalNode.current === node) {
        /* @HINT: No need to re-run `showModal()` again while modal 
          is already visible prior */
        return modalRef.current.id;
      }

      modalNode.current = node;

      setModalVisibilityState("visible");

      return controls.show(
        React.cloneElement(node, { id }),
        modalRef,
        () => setModalVisibilityState(
          (prevModalVisibilityState) => {
            if (prevModalVisibilityState === "visible") {
              return "hidden";
            }
            return prevModalVisibilityState;
          }
        )
      );
    },
    closeModal (id?: string) {
      if (modalRef.current) {
        setModalVisibilityState("hidden");
        controls.close(id || modalRef.current.id);
        modalRef.current = null;
      }
    }
  };
};

Step 2: create the context and provider for the modal

import React from 'react';

type ModalControls = {
  show: (node: React.ReactNode, reference: React.MutableRefObject, callback: (() => void)) => string,
  close: (modalId: string) => void;
};

export const ModalControlsContext = React.createContext<ModalControls | null>(null);

export const ModalControlsProvider = ({ children, styles = { className: "", wrapperClassName: "" } }: { children: React.ReactNode, styles: {
  className: string, wrapperClassName: string
} }) => {
  const [ modals, controls ] = useModalCore(styles);

  return (
    <ModalControlsContext.Provider value={controls}>
     {modals} {children}
    </ModalControlsContext.Provider>
  )
};

Step 3: Create the access hook for showing/closing modal via exposed APIs (final step)

import React, { useContext } from 'react';
import { ModalControlsContext } from './ModalControlsContext';
import { useModalControls } from './useModalHooks';

export const useModal = (modalId: string) => {
  const controls = useContext(ModalControlsContext);
  return useModalControls(controls, modalId);
}

// const { showModal, closeModal, isModalVisible } = useModal("Confirmation_Delete_Task");

Let's take a look at creating a compound dropdown component that uses no React state and no context

Step 1: Create a hook to handle dropdown UI state in both React and the DOM

import { useState, useRef, useCallback } from 'react';
import { useBus, useComposite } from 'react-busser';

export const useDropdownCore = (items = [], key, dropDownEventName) => {
  const itemsCopy = items.slice(0);
  const  [bus] = useBus({
    fires: [dropDownEventName],
    suscribes: []
  }, key);
  const dropdownRef = useRef(new Map()).current;
  const [composite, handleUpdatesFactory] = useComposite(
    "__dropdown:menu:change",
    (prevComposite, nextComposite) => {
      return {
        ...prevComposite,
        ...nextComposite
      }
    },
    {
      selectedIndex: -1,
      selectedItem: null
    },
    key
  );

  useEffect(() => {
    /* @HINT: Trigger single/stream braodcast in the cascade chain */
    bus.emit(dropDownEventName, { composite, key });
  /* eslint-disable-next-line react-hooks/exhaustive-deps */
  }, [bus, composite.selectedIndex, dropDownEventName, key]);

  const onSelectedItemChange = handleUpdatesFactory("__dropdown:menu:change");

  const handleKeys = useCallback(() => undefined, []);

  const toggleOpenState = useCallback(() => {
    const dropdownListNode = dropdownRef.get(key);

    if (dropdownListNode) {
      dropdownListNode.classList.toggle("show-list");
    }
  /* eslint-disable-next-line react-hooks/exhaustive-deps */
  }, [key])

  const setSelectedItem = useCallback((index) => {
    const dropdownListNode = dropdownRef.get(key);

    if (dropdownListNode) {
      dropdownListNode.classList.remove("show-list");
    }

    onSelectedItemChange({
      selectedIndex: index,
      selectedItem: itemsCopy[index]
    });
  /* eslint-disable-next-line react-hooks/exhaustive-deps */
  }, [key, itemsCopy.map(item => (item.id || item.value || item.text)).join('|')]);

  return {
    composite,
    handleKeys,
    dropdownRef,
    toggleOpenState,
    setSelectedItem
  };
};

Step 2: Implement the compound components

import React, { useEffect } from "react";
import pick from "lodash.pick";

import { useDropdownCore } from "./hooks";

const hasChildren = (children, count) => {
  const childCount = React.Children.count(children);
  return childCount === count;
};

const Trigger = ({
  as: Component = "button",
  children,
  className,
  style,
  ...props
}) => {
  const getLabelText = (selectedItem, defaultText, children) => {
    const noChild = hasChildren(children, 0);

    if (!noChild) {
      if (selectedItem) {
        return selectedItem?.text || "<unknown>";
      }
      return children || defaultText;
    }

    return selectedItem
      ? selectedItem?.text || "<unknown>"
      : defaultText || "Select an item...";
  };

  return (
    <Component
      tabIndex={0}
      key={props.placeholder}
      onClick={() => props.onTriggerClick()}
      className={className}
      role={Component === "button" ? undefined : "button"}
      style={style}
    >
      {getLabelText(
        props.composite.selectedItem,
        props.placeholder,
        children
      )}
    </Component>
  );
};

const ListItem = ({
  as: Component = "li",
  children,
  className,
  style,
  ...props
}) => {
  return (
    <Component className={className} style={style} role="listitem" {...props}>
      {children}
    </Component>
  );
};

const List = ({
  as: Component = "ul",
  children,
  className,
  style,
  render,
  items,
  ...props
}) => {
  const noChild = hasChildren(children, 0);
  return (items.length > 0 ? (
    <Component
      className={className}
      style={style}
      role="listbox"
      ref={props.innerRef}
      items={Component === "ul" || Component == "ol" ? undefined : items}
      composite={Component === "ul" || Component == "ol" ? undefined : props.composite}
      onClick={Component === "ul" || Component == "ol" ? undefined : ('onListItemClick' in props) && props.onListItemClick || undefined}
    >
      {noChild
        ? items.map((item, index) => (
            <ListItem
              key={String((item.id || item.text) + "_" + index)}
              selected={index === props.composite.selectedIndex}
              onClick={() => ('onListItemClick' in props) ? props.onListItemClick(index) : undefined}
            >
              {
                typeof render === "function"
                ? render(item, index === props.composite.selectedIndex)
                : item.text
              }
            </ListItem>
          ))
        : children({
          items,
          composite: props.composite,
          onClick: ('onListItemClick' in props) && props.onListItemClick || undefined
        })
      }
    </Component>
    ) : null
  );
};

const Dropdown = ({
  items = [],
  placeholder = "",
  onChange = () => undefined,
  tabIndex,
  name,
  id,
  className,
  children
}) => {
  const isSubChild = (child, tag) =>
    React.isValidElement(child) && String(child?.type).includes(tag);

  const renderChildren = (children, extraChildProps) => {
    const oneChild = hasChildren(children, 1);
    const noChild = hasChildren(children, 0);

    if (noChild || oneChild) {
      console.error("[Error]: <Dropdown /> requires no less than 2 valid children; <Dropdown.Trigger /> and <Dropdown.List />");
      return null;
    }

    const childrenList = React.Children.toArray(children);

    if (typeof children === "object") {
      if (children !== null && Array.isArray(childrenList)) {
        return childrenList.map((child) => {
          if (!("props" in child)) {
            return null;
          }

          switch (true) {
            case isSubChild(child, "Trigger"):
              return React.cloneElement(
                child,
                pick(extraChildProps, [
                  "onTriggerClick",
                  "placeholder",
                  "composite"
                ])
              );

            case isSubChild(child, "List"):
              return React.cloneElement(
                child,
                Object.assign(
                  {},
                  pick(extraChildProps, [
                  "items",
                  "onListItemClick",
                  "composite"
                ]), {
                  innerRef: (node) => {
                    return !node
                      ? extraChildProps.dropdownRef.delete(id)
                      : extraChildProps.dropdownRef.set(id, node);
                  }
                })
              );

            default:
              return React.isValidElement(child) ? child : null;
          }
        });
      }
    }

    return null;
  };

  const {
    composite,
    toggleOpenState,
    dropdownRef,
    handleKeys,
    setSelectedItem
  } = useDropdownCore(items, id, "$__dropdown:change:braodcast");

  useEffect(() => {
    if (composite.selectedIndex !== -1) {
      onChange(composite.selectedItem);
    }
  /* eslint-disable-next-line react-hooks/exhaustive-deps */
  }, [composite.selectedIndex]);

  return (
    <div name={name} id={id} tabIndex={tabIndex} onKeyDown={handleKeys} className={className}>
      {renderChildren(children, {
        items,
        placeholder,
        onTriggerClick: toggleOpenState,
        onListItemClick: setSelectedItem,
        composite,
        dropdownRef
      })}
    </div>
  );
};

Dropdown.Trigger = Trigger;
Dropdown.List = List;
Dropdown.ListItem = ListItem;

const DropdownEvent = {
  DROPDOWN_CHANGE_BROADCAST: "$__dropdown:change:braodcast"
};

export { Dropdown, DropdownEvent };

Step 3: Use the component and its' event

import  React, { useState, useEffect } from 'react';
import { Dropdown, event } from './components/Dropdown';
import './styles.css';

import { useBus } from 'react-busser';

export function DropdownBoard () {
  const getOrdinalSuffix = (num = 0, asWord = false) => {
    let ordinal = "th";

    if (num % 10 === 1 && num % 100 !== 11) {
      ordinal = "st";
    }
    else if (num % 10 === 2 && num % 100 !== 12) {
      ordinal = asWord ? "ond" : "nd";
    }
    else if (num % 10 === 3 && num % 100 !== 13) {
      ordinal = "rd";
    }

    return !num && num !== 0 ? '' : ordinal;
  };

  const getNumbering = (num = 0, asWord = false) => {
    const tens = [
      "zero",
      "fir",
      "sec",
      "thi",
      "four",
      "fif",
      "six",
      "seven",
      "eig",
      "nin",
      "ten",
      "eleven",
      "twelv",
      "thirteen",
      "fourteen",
      "fifteen",
      "sixteen",
      "seventeen",
      "eighteen",
      "nineteen"
    ];
    const hundreds = [
      "",
      "",
      "twentee",
      "thirtee",
      "fortee",
      "fifthee",
      "sixtee",
      "seventee",
      "eigh",
      "nine"
    ];

    if ((num.toString()).length > 9) {
      return "overflow";
    }
      
    const numString = ("000000000" + num).substr(
      -9
    ).match(
      /^(\d{2})(\d{2})(\d{2})(\d{1})(\d{2})$/
    );
      
    if (!numString) {
      return ""; 
    }

    const [ , first, second, third, fourth, fifth ] = numString;
      
    let numberingString = "";

    numberingString += (Number(first) !== 0) ? (tens[Number(first)] || hundreds[Number(first[0])] + " " + tens[Number(first[1])]) + "crore " : "";
    numberingString += (Number(second) !== 0) ? (tens[Number(second)] || hundreds[Number(second[0])] + " " + tens[Number(second[1])]) + "lakh " : "";
    numberingString += (Number(third) !== 0) ? (tens[Number(third)] || hundreds[Number(third[0])] + " " + tens[Number(third[1])]) + "thousand " : "";
    numberingString += (Number(fourth) !== 0) ? (tens[Number(fourth)] || hundreds[Number(fourth[0])] + " " + tens[Number(fourth[1])]) + "hundred " : "";
    numberingString += (Number(fifth) !== 0) ? ((numberingString !== "") ? "and " : "") + (tens[Number(fifth)] || hundreds[Number(fifth[0])] + " " + tens[Number(fifth[1])]) + getOrdinalSuffix(num, asWord) : "";
    
    return numberingString;
  };
  const [dropDownDetails, setDropDownDetails] = useState(() => ({
    key: "__dropdownId_32049",
    composite: { seletedIndex: -1, selectedItem: null }
  }));
  const [ bus ] = useBus({
    fires: [],
    subscribes: [event.DROPDOWN_CHANGE_BROADCAST]
  });

  useEffect(() => {
    const callBack = ({ key, composite }) => {
      setDropDownDetails((prevDropDownDetails) => {
        switch (true) {
          case key === dropDownDetails.key:
            return {
              ...prevDropDownDetails,
              composite
            };
          default:
            return prevDropDownDetails;
        }
      });
    };
  
    bus.on(event.DROPDOWN_CHANGE_BROADCAST, callBack);

    return () => {
      bus.off(callBack);
    }
  /* eslint-disable-next-line react-hooks/exhaustive-deps */
  }, [dropDownDetails.key, bus]);

  return (
    <div>
      Dropdown Component with key =
      {dropDownDetails.key} 
      was changed to 
      {dropDownDetails.composite.selectedIndex === -1
        ? "an unknown"
        : `the ${getNumbering(dropDownDetails.composite.selectedIndex + 1, true)}`}
      value
    </div>
  )
}

export function Dropdowns() {
  return (
    <div className="AppDropdown">
      <Dropdown
        className="dropdown"
        onChange={() => {
          console.log("hello");
        }}
        id={"__dropdownId_95014"}
        items={[{ text: "Apple" }, { text: "Orange" }]}
        placeholder="Select a fruit >"
      >
        <Dropdown.Trigger className="dropdown-trigger" />
        <Dropdown.List
          className="dropdown-list"
          render={(itemNode, selected) => {
            return (
              <span style={selected ? { color: "red" } : undefined}>
                {itemNode.text}
              </span>
            );
          }}
        />
      </Dropdown>

      <Dropdown
        className="dropdown"
        onChange={(selectedItem) => {
          console.log("hello", selectedItem);
        }}
        id={"__dropdownId_32049"}
        items={[{ text: "Apple" }, { text: "Orange" }, { text: "Grape" }, { text: "Mango" }]}
        placeholder="HelloWorld"
      >
        <Dropdown.Trigger className="dropdown-trigger-ns">
          {"Select any sweet fruit:"}
        </Dropdown.Trigger>
        <Dropdown.List
          className="dropdown-list"
          as={({ items, composite, onClick, ...props }) => {
            return (
              composite.isOpen && (
                <ol {...props}>
                  {items.map((item, index) => {
                    return (
                      <li
                        key={String(index)}
                        data-selected={index === composite.selectedIndex}
                        onClick={() => (onClick ? onClick(index) : undefined)}
                      >
                        {item.text}
                      </li>
                    );
                  })}
                </ol>
              )
            );
          }}
        />
        </Dropdown>
    </div>
  );
}

Finally, an example of how to use the useSharedState() hook from react-busser

import React, { useCallback } from "react";
import { useSharedState } from "react-busser";

/* @USAGE: */

const TodosComponent = () => {
  const [sharedState, setSharedState] = useSharedState();
  
  const handleClick = () => {
    setSharedState({
      slice: "list",
      value: [1,2,3]
    });
  };
  
  return <div onClick={handleClick}>{String(sharedState.list)} CLICK ME!</div>
}

export default TodosComponent;

Cascade Broadcasts

Cascade broadcasts sets up the stage for the evented object system which react-busser provides by turning each React component to an evented object via the event bus. It ensures that the UI updates are predictable and that all events (from each event bus) fires in a well-timed fashion every single time. Also, there are well placed constraints to ensure that events are never fired out-of-order. The result is several interconnected perfect cycles of UI updates.

Some of these constraints promoted by the Cascade Broadcasts are as follows:

ReactJS props should only be used to deliver base or derived state data or state-altering callbacks from exactly one parent component to exactly one child and never to pass data across sibling components (via a parent component) or pass derived state data.
ReactJS context should never be mutated in place (lest it causes unwanted re-renders). It's best to use refs (useRef()) together with context (useContext()) and not context alone.
Events are always fired in a cascaded (successive) manner and never indiscriminately. useEffect() is usually used to implement this cascade of events.
There's no need to lift state at all!
Most of the logic used for conditional rendering is best situated inside a ReactJS hook which leaves the JSX much cleaner and readable.
Render props can now render mostly as pure, presentation JSX mostly.

Before you can setup cascade braodcasts, you have to be able to create a pair of custom ReactJS hooks where one of the pair makes use of useBus() to setup an event bus to trigger a broadcast. The broadcast can be a one-time thing or a stream. A single pair of ReactJS Hooks are responsible for either a one-time broadcast a single stream of braodcasts. This pair is made up of:

A source hook
A target hook

The source hook make use of useBus() to emit a one-time broadcast or streamed braodcast which is listened for by the target hook. The react-busser library exposes a collection of basic hooks that can be used to build other custom pair of hooks as follows:

Data Primitives

A Data primitive is the most basic data form that can be used to represent and structure data for use within a client-side rendered web application. Busser defines only 3 primitives that can be used in specific situations an they are packagedd as ReactJS hooks.

useCount(): used for any kind of state that involves a counter
useList(): used for any kind of state that involves a list
useProperty(): used for any kind of state with a finite set of string values
useComposite(): used for any kind of state that involes updates made up of derived state from base state.

Signals variants

There are signals variants to all the data primitive reactJS hooks for react-busser as well

useSignalsCount(): similar to useCount() but makes use of signals under the hood.
useSignalsList(): similar to useList() but makes use of signals under the hood.
useSignalsComposite(): similar to useComposite() but makes use of signals under the hood.

Let's look at some real-world use cases of how to actualize cascade broadcasts to manage state using paired ReactJS hooks:

Assuming we would like build an e-commerce site, we want to be able to manage Cart state. We need a centralised place (A React Component) to store this state but not in a global scope or using a global variable or global state. We need a local scope residing inside of a ReactJS hook. However, we want to be able to be notified of any changes to the Cart state anywhere else (Another React Component). How do we actualize this using react-busser ?

Well, we start by thinking about what a Cart state is and what it looks like. A Cart is a list of products that a user has selected with their respective quanities all tracked towards a purchase (checkout).

Without react-busser, one can choose to build a solution like this one but the problem with it is that:

It loads reusable code logic where it's not needed.
It relies heavily on event listeners as function props which tightly couple a parent component data needs to it's child component.
It requires it's own context provider (a lot of the time this can lead to a very nested mess of providers known as Provider (React Context) hell).

We can take another approach with the react-busser way.

If we think about it well enough, the basic hook that suits our source hook is the useList() since a Cart is a list of products. Below, code to manage the Cart state is written as follows:

SOURCE HOOK 👇🏾👇🏾

import { useEffect, useCallback } from "react";
import { useBus, useList, useBrowserStorage, useSharedState } from "react-busser";

const EVENTS = { UNSET_CART: "unset:cart", ADD_TO_CART: "add:shopping:cart:item", REMOVE_FROM_CART: "remove:shopping:cart:item", EMPTY_CART: "empty:shopping:cart", INCREASE_CART_ITEM_QUANTITY_COUNT: "increment_quantity:shopping:cart:item", DECREASE_CART_ITEM_QUANTITY_COUNT: "decrement_quantity:shopping:cart:item", SET_CART_UPDATES: "set:shopping:cart:updates", RESET_CART_UPDATES: "reset:shopping:cart:updates", TRIGGER_EMPTY_CART: "shadow;empty:cart", TRIGGER_INCREASE_CART_ITEM_QUANTITY_COUNT: "shadow;increment:cart:item:quantity" };

export const useCart = ( initial, name, { maximumCartSize, itemPropForIdentity, itemPropForPrice, itemPropForQuantity }, bus ) => { const { getFromStorage, setToStorage } = useBrowserStorage({ storageType: "local" }); const cartReducer = (prevList, { productItem, quantityValue }, event) => { let nextList = prevList.slice(0); const index = prevList.findIndex( (listItem) => productItem && listItemitemPropForIdentity === productItemitemPropForIdentity ); / @HINT: Clone the product item so we can create a cart item out of it / const cartItem = ("structuredClone" in window) ? window.structuredClone(productItem) : JSON.parse(JSON.stringify(productItem));

const quantity = cartItem[itemPropForQuantity];
const price = cartItem[itemPropForPrice];
const calculateUniqueItemsCount = prevList.length;

switch (event) {
  case EVENTS.ADD_TO_CART:
    if (calculateUniqueItemsCount > maximumCartSize) {
      throw new Error("useCart[Error]: maximum cart size exceeded!");
    }

    if (!quantity || typeof quantity !== "number") {
      cartItem[itemPropForQuantity] = quantityValue || 1;
    }

    nextList = nextList.concat([cartItem]);
    break;
  case EVENTS.REMOVE_FROM_CART:
    nextList.splice(index, 1);
    break;
  case EVENTS.INCREASE_CART_ITEM_QUANTITY_COUNT:
    if (typeof cartItem[itemPropForQuantity] !== "number") {
      thorw new Error("useCart[Error]: cart item has no quanity to increment");
    }

    ++cartItem[itemPropForQuantity];
    nextList.splice(index, 1, cartItem);
    break;
  case EVENTS.DECREASE_CART_ITEM_QUANTITY_COUNT:
    if (typeof cartItem[itemPropForQuantity] !== "number") {
      thorw new Error("useCart[Error]: cart item has no quanity to decrement");
    }

    --cartItem[itemPropForQuantity];
    nextList.splice(index, 1, cartItem);
    break;
  case EVENTS.UNSET_CART:
    /* @HINT: reset the cart state back to its initial state */
    nextList = initial;
    break;
  default:
    /* @HINT: this default case deals with EVENTS.EMPTY_CART event*/
    nextList = [];
    break;
}

return nextList;

};

const cartList, ...rest = useList( EVENTS.UNSET_CART, EVENTS.ADD_TO_CART, EVENTS.REMOVE_FROM_CART, EVENTS.INCREASE_CART_ITEM_QUANTITY_COUNT, EVENTS.DECREASE_CART_ITEM_QUANTITY_COUNT, EVENTS.EMPTY_CART , cartReducer, getFromStorage(name, initial), name );

useEffect(() => { let eventName = EVENTS.SET_CART_UPDATES;

if (cartList.length === 0) {
  eventName = EVENTS.RESET_CART_UPDATES;
}

const wasSaved = setToStorage(name, cartList.slice(0));

if (wasSaved) {
  /* @HINT: Trigger single/stream braodcast in the cascade chain */
  bus.emit(eventName, cartList.slice(0));
}

}, [bus, (cartList.map((cart) => cartitemPropForIdentity).join('|'))]);

return cartList, ...rest; };

/ At this point, it's time to create a hook that houses our business logic for managing a shopping cart /

export const useCartManager = (initial = [], name) => { const cartConfig = useSharedState("cartConfig"); const { itemPropForIdentity } = cartConfig;

/* @EXAMPLE:

cartConfig = { maximumCartSize = 20, itemPropForIdentity = "id", itemPropForPrice = "price", itemPropForQuantity = "qty" }

/ @HINT: Setup event bus for triggering broadcasts for the useCart() hook / const bus = useBus( { fires: EVENTS.SET_CART_UPDATES, EVENTS.RESET_CART_UPDATES, subscribes: EVENTS.TRIGGER_EMPTY_CART, EVENTS.TRIGGER_INCREASE_CART_ITEM_QUANTITY_COUNT }, name ); const cartList, cartListUpdateFactory = useCart( initial, name, cartConfig, bus );

const argumentsTransformFactory = (quantityValue) => (product) => ({ productItem: product, quantityValue });

const addItemToCart = cartListUpdateFactory( EVENTS.ADD_TO_CART, argumentsTransformFactory(1) ); const addItemToCartDoubleQuantity = cartListUpdateFactory( EVENTS.ADD_TO_CART, argumentsTransformFactory(2) ); const removeItemFromCart = cartListUpdateFactory( EVENTS.REMOVE_FROM_CART, argumentsTransformFactory() ); const emptyCart = cartListUpdateFactory(EVENTS.EMPTY_CART); const incrementCartItemQuantity = cartListUpdateFactory( EVENTS.INCREASE_CART_ITEM_QUANTITY_COUNT, argumentsTransformFactory() ); const decrementCartItemQuantity = cartListUpdateFactory( EVENTS.DECREASE_CART_ITEM_QUANTITY_COUNT, argumentsTransformFactory() );

const cartLength = cartList.length;

const isAddedToCartAlready = useCallback((product) => (Boolean(cartList.find((listItem) => { return listItemitemPropForIdentity === productitemPropForIdentity }))), itemPropForIdentity, cartLength);

const clickHandlerFactory = useCallback((product) => { return !isAddedToCartAlready(product) ? () => addItemToCart(product) : () => removeItemFromCart(product) / eslint-disable-next-line react-hooks/exhaustive-deps / }, []);

useEffect(() => {

const emptyCartShadowHandler = () => emptyCart();
const incrementCartQuantityShadowHandler = (product) => incrementCartItemQuantity(product);

/* @NOTE: There are times where we want an action to be able to be triggered from multiple
    CTAs/button clicks/interactions on the UI instead of just one CTA/button click; In those 
    times we make use of #ShadowEvents: events that triggers another event on the cascade 
    of event(s) broadcasted
*/

/* @HINT: Shadow events */

bus.on(EVENTS.TRIGGER_EMPTY_CART, emptyCartShadowHandler);
bus.on(EVENTS.TRIGGER_INCREASE_CART_ITEM_QUANTITY_COUNT, incrementCartQuantityShadowHandler);

return () => {
  bus.off(emptyCartShadowHandler);
  bus.off(incrementCartQuantityShadowHandler);
}

/ eslint-disable-next-line react-hooks/exhaustive-deps / }, []);

return { emptyCart, addItemToCartDoubleQuantity, incrementCartItemQuantity, decrementCartItemQuantity, clickHandlerFactory, isAddedToCartAlready, }; }

The ReactJS hook above is the `useCart()` hook which is also the **source hook**. It will manage the **Cart** state directly. But we are not done. We still need the second ReactJS hook in the pair which will be used to recieve updates. Both ReactJS hooks can be defined once and used in one or many other ReactJS projects that make use of **react-busser**.

Again, below, code to manage the **Cart** state updates is written as follows:

>TARGET HOOK 👇🏾👇🏾
```javascript
import { useEffect } from "react";
import { useComposite } from "react-busser";

const EVENTS = {
  UNSET_CART: "unset:cart",
  ADD_TO_CART: "add:shopping:cart:item",
  REMOVE_FROM_CART: "remove:shopping:cart:item",
  EMPTY_CART: "empty:shopping:cart",
  INCREASE_CART_ITEM_QUANTITY_COUNT: "increment_quantity:shopping:cart:item",
  DECREASE_CART_ITEM_QUANTITY_COUNT: "decrement_quantity:shopping:cart:item",
  SET_CART_UPDATES: "set:shopping:cart:updates",
  RESET_CART_UPDATES: "reset:shopping:cart:updates",
  TRIGGER_EMPTY_CART: "shadow;empty:cart",
  TRIGGER_INCREASE_CART_ITEM_QUANTITY_COUNT: "shadow;increment:cart:item:quantity"
};

export const useCartUpdates = (
  initial = {
    augumentedCartList: [],
    totalAmountInCartList: 0,
    totalQuantityInCartList: 0,
    totalCountInCartList: 0
  },
  name,
  { itemPropForPrice, itemPropForQuantity }
) => {
  const compositeReducer = (prevComposite, cartList, event) => {
    let nextComposite = { ...prevComposite };

    const calculateItemTotals = cartList.map((listItem) => ({
      ...listItem,
      itemTotal: listItem[itemPropForPrice] * listItem[itemPropForQuantity]
    }));

    const calculatedTotal = cartList.reduce(
      (total, listItem) =>
        total + listItem[itemPropForQuantity] * listItem[itemPropForPrice],
      0
    );

    const calculatedTotalItems = cartList.reduce(
      (sum, listItem) => sum + listItem[itemPropForQuantity],
      0
    );

    const calculateUniqueItemsCount = cartList.length;

    switch (event) {
      case EVENTS.SET_CART_UPDATES:
        nextComposite = {
          ...nextComposite,
          augumentedCartList: calculateItemTotals,
          totalAmountInCartList: calculatedTotal,
          totalQuantityInCartList: calculatedTotalItems,
          totalCountInCartList: calculateUniqueItemsCount
        };
        break;
      default:
        /* @HINT: this default case deals with EVENTS.RESET_CART_UPDATES event*/
        nextComposite = initial;
        break;
    }

    return nextComposite;
  };

  return useComposite(
    [EVENTS.SET_CART_UPDATES, EVENTS.RESET_CART_UPDATES],
    compositeReducer,
    initial,
    name
  );
};

Now that we have a pair of source and target hooks, we can now start managing state.

import React, { useCallback } from "react";
import { useCartManager } from "libs/hooks/cart";

import "./ProductList.css";

const EVENT_TAGS = {
  component: {
    PRODUCTLIST: "ProductList.component",
    PRODUCT: "Product.component",
    SHOPCARTCOUNTER: "ShopCartCounter.component",
    SHOPCARTCHECKOUT: "ShopCartCheckout.component",
  }
};

const ProductList = ({
  /* @NOTE: all list of products */
  products = [],
  /* @NOTE: logged-in users' shopping cart from last session */
  cart = []
}) => {

  /* @HINT: One-liner to manage a shopping cart 😊 */
  const { clickHandlerFactory, isAddedToCartAlready } = useCartManager(
    cart,
    EVENT_TAGS.component.PRODUCTLIST
  );

  const getButtonActionTextForCartUpdates = (product) => {
    return isAddedToCartAlready(product) ? "Remove From Cart" : "Add To Cart"
  }

  return (
    <>
      {products.length === 0 ? (
        <p className={"products_empty_msg"}>No products found!</p>
      ) : (
         <ul className={"product_list"}>
            {products.map((product, index) => {
                const ctaClickHandler = clickHandlerFactory(product);
                return (
                  <li key={String(index)}>
                    <h4>{product.name}</h4>
                    <figure className={"product_display"}>
                      <img alt={product.image.description} src={product.image.source} />
                      <span>{product.price}</span>
                    </figure>
                      <div className={"product_call_to_action"}>
                        <button onClick={ctaClickHandler}>
                          {getButtonActionTextForCartUpdates(product)}
                        </button>
                      </div>
                  </li>
                );
            })}
         </ul>
      )}
   </>
 );
}

Shadow Events

Shadow events work along with the concept of cascade broadcasts. They make it possible to

They are events that are setup to handle events triggered from a React component other than the component that houses the *source hook. They are used to centralize the logic for specific events that enable a cascade broadcast to loop back to it's last bbroadcast origin.

Ideas borrowed from Redux

There are a couple of ideas that busser borrows from Redux. These ideas are crucial to the manner busser works in general.

Reducers
Actions (Synchronous ONLY)
A Store

Ideas borrowed from Jotai

There are also a couple of ideas that busser orrows from Jotai.

Atom

Example(s)

Here is an example (screenshot) of a simple todo app built using react-busser. It uses 2 custom ReactJS hooks (useTodoList() and useTodoCounter()) that do the job of managing the todo list state data and todo count state data respectively.