 Resources from Daishi Kato in 2024

Jotai's state management is primitive and flexible. This gives you room to build, compose, and share state throughout your application exactly how you need it.

This flexibility can become hard to manage when you have complex requirements that span across a number of states your application can be in.

Jotai lets you leverage other state management solutions through integrations so that you can solve the problem you're facing exactly how you need to.

One of those integrations is XState. XState gives you a safe abstraction to enumerate and handle the complex states your application can be in.

With Jotai + XState, you get the flexibility and ease of use of Jotai with the power of XState.

XState is a sophisticated library to provide a better and safer abstraction for state management. 

React is one of the web’s most popular frameworks for building JavaScript applications. 

If you know what you’re doing, React can drastically simplify how you build, use, and maintain code.

Whether you’re a React newbie or you’re ready for advanced techniques, you can level-up with egghead. Explore our in-depth courses, lessons, and community resources to build more powerful applications and crack open your career.

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Complex State Management in React with Jotai and XState

jotai is a primitive and flexible state management solution for React. 

jotai gives you a minimalistic API that you can use that separates your state management from your UI. You get the benefits of well manages state AND you don't have to set up any boilerplate like defining actions, reducers, dispatchers, or stores. 

You create an atom and you're off to the races managing your application state.

In this course, you'll build an SVG drawing application. You'll see how you can represent the canvas as state through atoms and add svg path, change the path colors, delete, and even undo actions. You'll sum up your learning by learning how jotai can isolate state in your applications by using and composing Providers.

You'll be able to use the concepts you learn here to manage any state in your own application.

Manage Application State with Jotai Atoms

Zustand is a state management library aimed at staying simple and un-opinionated so that you as the developer can build your application as you see fit. To do this it creates a store (module of state) that you can subscribe components to read and update data from.

Zustand leans on hooks as the primary way to interact with your state. This means you get less boilerplate and a centralized, action-based state management solution that scales with the complexity of your app.

Daishi, a core contributor of Zustand, will show you the inner workings of the library by creating a small version of it. You learn how Zustand's API came to be and gain a better understanding of it by the end of this course.

Create a Zustand-like Module State Library

Jotai is a state management library for React. You will learn how it can be used instead of useState for shared state.

We'll start with two `Counter` components that each have their own React `useState` instance which isolates the state to that component. To share state, we'll create an `atom` from jotai and replace the `useState` calls to `useAtom`, and that's it, you have shared state.


Share State Between React Components with Jotai useAtom

Derived atoms can be created from other atoms. To do so, you pass a read function as the first argument which is traditionally called `get`. this will allow you to retrieve any other atom and transform the data received. 

The derived atom can be used just like a normal atom but this way lets you easily separate logic outside of a component.

Derive State from a Jotai Atom in React

We have a naive SVG app that can draw dots onto a canvas as the mouse scrolls over. You’ll notice as you drag the mouse around the canvas that the commit count in the top left corner increases. This is because the SVG component rerenders on every dot that’s drawn.

The rerenders are due to the fact that we are using the `dotsAtom` directly in the component. This is where write-only atoms come in handy. They can receive a write function that will handle the updates to your atom state which will fix the rerender issue.

We will also cover how to compose write-only atoms to add functionality.

Prevent Rerenders and Add Functionality with Jotai Write-only Atoms

Right now, the app that we have built draws dots on SVG on canvas. As you start applications you'll often find working in one file works the best to build something quickly. There comes a point when you need to move code out of the single file and structure it.

First, we'll see how the app has been refactored into 3 files. We are able to export the atoms and components that are needed throughout our app while keeping internal logic isolated in the file meaning not all atoms are exported.

Next, we'll create a new atom that takes a set of points and generates a path. You'll see how to create new functionality through an atom and import it into another component that's using Jotai atoms.

Structure Jotai Atoms and Add Functionality to a React App

In the previous lessons, we’ve been able to create and render shapes by storing the data needed into a Jotai atom. You’ll notice that each time you draw a path that the previous path is cleared. This is because we are setting the new path in the old path’s place, it's gone forever.

We can preserve state by aggregating atoms into another single atom by pushing them into an array. Once we have this array, we can map over the array in a new component to draw as many paths as you would like

Preserve State by Combining Multiple Jotai Atoms into One Atom

Atoms can take just about anything as input, this includes other Atoms as well! You will see how we can take an atom, `ShapeAtom`, as input so that we can highlight the shape that we select.

To do this, we will need to export two functions for you to consume elsewhere. One that sets the the input (an atom) as the atom contained within our newly created atom. The other function will determine if a current shape is selected or not. This will be done by deriving the selected atom from our newly created atom and returning a boolean if it matches the original shape.

With these two functions we can apply additional styles to shapes that are selected.

Add Additional Functionality by Creating Jotai Atoms that Hold Atoms

We added the ability to select an SVG by creating a new atom that holds an atom that you select. With this we can build additional functionality like setting the color of the SVG path.

In this lesson, we will update ShapeAtom to have an optional `color` property and create a new atom to set that property. You'll see how we can create a `Controls` Component that will interact with an SVG Path component through the `setColorAtom` atom. We can get the currently selected path with `selectedShapeAtomAtom` and control the properties of the atom within.

Compose Jotai Atoms to Update Atom Values From Different React Components

We will look at how to delete a shape that we have stored in an array. You'll see how we can continue building functionality by composing atoms together to achieve what we want. 

For this feature, we will need to create a few atoms to add the functionality needed. We will start by creating `selectedAtom` and `unselectAtom`. `selectedAtom` is a getter for the selected Shape and `unselectAtom` will be used to clear the selection when an atom is deleted.

When these two functions are set, we can create a `deleteSelectedShapeAtom` which will filter out the selected atom that is held in `shapeAtomsAtom`.  And finally, we'll wire this up to a button to actually use!  

Delete Data in a Jotai Atom by Composing and Filtering Atoms

Often times you'll want the user of your application to be able to undo an action that they've taken. Adding this feature requires you to keep track of the actions that have occurred and what state the application was in at each action. 

To solve this, you'll need to store the history in some way. With Jotai, because the atoms that you are using are immutable you can save a snapshot of an atom when an action is taken and store that for use later on.

We will replace the previous `shapesAtomsAtom` that stored the array of our svg shapes with a `historyAtom` that will add each snapshot of the canvas to an array. We can then export a new `shapesAtomsAtom` that will behave exactly like the previous one as well as a `saveHistoryAtom` that we can use when we update our state. This will allow implementing an `undoHistory` atom that will remove any shapes or colors that we don't want to use on our canvas.

Undo Actions on State by Implementing an undoHistory Feature with Jotai Atoms

Now that we have a lot of functionality finished for this example, we'd like to create multiple components (or multiple canvases) that you can draw on.

You'll notice that if you do that right now, drawing on one will draw on the other because state is global to the entire application.

Jotai exposes a `Provider` component that allows you to wrap any part of your application that you want to isolate state to.


Isolate State in an Application with Jotai Provider

Jotai has a primitive and flexible API, because of this it's up to you on how you manage your state within an atom. 

Sometimes your state is complex enough to warrant a sophisticated library for safer abstraction. This is where you can install xstate to your application and Jotai will work seamlessly with the state machines that you define using `atomWithMachine`.

This allows you to consume the machine like any other atom in your components with `useAtom`. 

As an added bonus, I'll show you how to use xstate's visualizer to develop and interact with your state machine in dev tools. 


Handle Complex State in Jotai with XState using atomWithMachine

Sometimes you need to display values in specific ways throughout your application based on the state that you are managing. The way to do this is to derive your state so you don't have to track multiple stateful items.

In Jotai, this is accomplished by creating an atom, getting the value from another atom that you are managing (in this case from Xstate), and using that value how you need it in your derived atom. This atom will be re-evaluated every time the managed state changes.

This pattern is great to use if you have complex state managed in something like Xstate but need a derived state value that is not strongly tied to that managed state. The pattern works the same for async and synchronous function calls as well as pulling in multiple atoms and libraries to use in your derived state.


Derive Jotai Atom State from Complex State Managed in Xstate 

When you reuse a component, there are times when you’d like that state to share the same values as other instances of that state. In other cases, you want to isolate your state.
With Jotai, you only need to wrap your components that you want to share state in Jotai’s `<Provider>` component the subsequent atom (and XState machine) state is shared for those components.

Share and Isolate XState State using Jotai Provider

We currently have a machine that displays a circle of green. When you click it, it will cycle through green, yellow, and Red.

What if you wanted to pass XState initial values from Jotai, you'll need to use the `initialValues` prop on Jotai Provider and pass a list of pair (atom and value) to it.

To do this we'll refactor the creation of the lightMachine to be a function that accepts an atom as an initial value.

One note to be aware of is that this initial value will only be set when the XState machines instantiate.


Provide XState with Initial Values through Jotai Provider

Statecharts are a formalism for modeling stateful, reactive systems. This is useful for declaratively describing the behavior of your application, from the individual components to the overall application logic.

xstate

Sometimes adding initial values through the jotai Provider is not what you want. Provider will create a whole new store with atom values

One way to initialize a state machine inside Jotai is to turn our initial `lightAtom` into a function `createLightAtom`. This function will take an `initial` property that we can pass to `createLightMachine` when we declare the function. We will then useEffect to initialize our lightMachine.

There is a small limitation with this pattern, the machine is initialized with it's default value and then over ridden with the value we pass in the effect. The initial render will use that default value while the second render will have the value we passed in.


Initialize a Xstate Machine with Jotai Atom in Atom Pattern

There are many cases where you want to share state between components in React. A lot of popular state management libraries implement this ‘module state’ for you such as Zustand.

We will implement a naive version of a `createStore` function that allows you to share your state between components in React.

`createStore` has a few functions that we return from it: `getState`, `setState`, and `subscribe`. Just like with React Hooks, we can get and set state within components. Because this is shared state, we need to give components a mechanism for updating when state changes in a separate component, that is where `subscribe` comes in. With the combination of these 3 functions, we can display and update a shared value between multiple components in React.

Share Module State Between Components in React Similar to Zustand

We have two components that use the same store. They display the data and update the store when a button is clicked. The logic in each component is the same and can be extracted into a custom hook

In this lesson, we'll extract the store logic into a `useStore` hook and use that custom hook like you would any other React hook. Then we'll extend the behavior of the hook to accept a function to update the previous state value.


Extract Module Logic (like Zustand) into a Custom React Hook

We have to functions right now. `createStore` that creates module state and `useStore` that consumes the module state that we created.

The logic is working as expected. State is being properly shared to the components that need it while still isolated from the rest of the app. The issue now is that we have extra re-renders in our application. Each component will rerender when any state changes

To fix this, we'll implement a selector function that will peek the value that you need out of state. This way only the components that depend on the value that is changed will re-render.


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Daishi Kato