State Management with React Hooks

State Management with React Hooks

In this session, you'll an understanding of the basics of using State Management with React Hooks. We are going to explore it and develop a custom Hook to manage global states — an easier to use method than Redux, and more performant than Context API.

In this session, you'll an understanding of the basics of using State Management with React Hooks. We are going to explore it and develop a custom Hook to manage global states — an easier to use method than Redux, and more performant than Context API.

The basics of React Hooks

If you are already familiar with React Hooks, you can skip this part.

useState()

Before Hooks, functional components had no state. Now, with the useState(), we can do it.

It works by returning an array. The first item of the above array is a variable that gives access to the state value. The second item is a function that updates the State Management of the component to reflect the new values on the DOM.

import React, { useState } from 'react';

function Example() {
  const [state, setState] = useState({counter:0});
  const add1ToCounter = () => {
    const newCounterValue = state.counter + 1;
    setState({ counter: newCounterValue});
  }

  return (
    <div>
      <p>You clicked {state.counter} times</p>
      <button onClick={add1ToCounter}>
        Click me
      </button>
    </div>
  );
}

useEffect()

Class components manage side effects using life cycle methods, like componentDidMount(). The useEffect() function lets you perform side effects in function components.

By default, effects run after every completed render. But, you can choose to fire it only when certain values have changed, passing an array of variables as a second optional parameter.

// Without the second parameter
useEffect(() => {
  console.log('I will run after every render');
});

// With the second parameter
useEffect(() => {
  console.log('I will run only when valueA changes');
}, [valueA]);

To have the same result as componentDidMount() we can send an empty array. Knowing that an empty set does never change, the effect will run only once.

// With empty array
useEffect(() => {
  console.log('I will run only once');
}, []);

Sharing states

We can see that Hooks states works exactly like class component states. Every instance of the component has its own state.

To work a solution which shares state between components, we will create a custom Hook.

The idea is to create an array of listeners and only one state object. Every time that one component changes the state, all subscribed components get their setState() functions fired and get updated.

We can do that by calling useState() inside our custom Hook. But, instead returning the setState() function, we add it to an array of listeners and return a function which updates the state object and run all listeners functions.

Wait. Isn’t this supposed to make my life easier?

Yes. I created a NPM package which encapsulates all this logic.

You will not need to this rewrite this custom hook on every project. If you just want to skip ahead and use the final solution, you can easily add it in your project by running:

npm install -s use-global-hook

You can learn how to use it by the examples in the package documentation. But, from now on, we are going to focus in how it works under the hood.

The first version
import { useState, useEffect } from 'react';

let listeners = [];
let state = { counter: 0 };

const setState = (newState) => {
  state = { ...state, ...newState };
  listeners.forEach((listener) => {
    listener(state);
  });
};

const useCustom = () => {
  const newListener = useState()[1];
  useEffect(() => {
    listeners.push(newListener);
  }, []);
  return [state, setState];
};

export default useCustom;

To use it on a component:

import React from 'react';
import useCustom from './customHook';

const Counter = () => {
  const [globalState, setGlobalState] = useCustom();

  const add1Global = () => {
    const newCounterValue = globalState.counter + 1;
    setGlobalState({ counter: newCounterValue });
  };

  return (
    <div>
      <p>
        counter:
        {globalState.counter}
      </p>
      <button type="button" onClick={add1Global}>
        +1 to global
      </button>
    </div>
  );
};

export default Counter;

This first version already works sharing state. You can add as many Counter components as you want in your application and it will all have the same global state.

But we can do better

What I didn’t like in this first version:

  • I want to remove the listener from the array when the component is unmounted.
  • I want to make it more generic, so we can use in other projects.
  • I want set a initialState by parameters.
  • I want to use more functional oriented programming.

Calling a function just before component unmount

We learned that calling the useEffect(function,[]), with an empty array, has the same use as componentDidMount(). But, if the function used in the first parameter returns another function, this second function will be fired just before the component is unmounted. Exactly like componentWillUnmount().

This is the perfect place to remove the component from the listeners array.

const useCustom = () => {
  const newListener = useState()[1];
  useEffect(() => {
    // Called just after component mount
    listeners.push(newListener);
    return () => {
      // Called just before the component unmount
      listeners = listeners.filter(listener => listener !== newListener);
    };
  }, []);
  return [state, setState];
};

The second version

Besides this last modification, we are also going to:

  • Set React as a parameter, not importing it anymore.
  • Not exporting the customHook but, exporting a function that returns a new customHook according to initialState parameter.
  • Create a store object that contains the state value and the setState() function.
  • Replace the arrow functions for regular functions in setState() and useCustom(), so we can have a context to bind the store to this.
function setState(newState) {
  this.state = { ...this.state, ...newState };
  this.listeners.forEach((listener) => {
    listener(this.state);
  });
}

function useCustom(React) {
  const newListener = React.useState()[1];
  React.useEffect(() => {
    // Called just after component mount
    this.listeners.push(newListener);
    return () => {
      // Called just before the component unmount
      this.listeners = this.listeners.filter(listener => listener !== newListener);
    };
  }, []);
  return [this.state, this.setState];
}

const useGlobalHook = (React, initialState) => {
  const store = { state: initialState, listeners: [] };
  store.setState = setState.bind(store);
  return useCustom.bind(store, React);
};

export default useGlobalHook;

Because we have a more generic Hook now, we have to setup it in a store file.

import React from 'react';
import useGlobalHook from './useGlobalHook';

const initialState = { counter: 0 };

const useGlobal = useGlobalHook(React, initialState);

export default useGlobal;

Separating actions from components

If you ever worked with complex state management library, you know that it is not the best idea to manipulate global state directly from the components.

The best way is to separate the business logic by creating actions which manipulate the state. For that reason I want that the last version of our solution doesn’t give component access to the setState() function, but a set of actions.

To work that out, our useGlobalHook(React, initialState, actions) function will receive an action object as a third parameter. Regarding that, there are somethings that I want to add:

  • Actions will have access to the store object. For that reason, actions may read the state with store.state, write state through store.setState() and even call other actions using state.actions.
  • For organization, the actions object may contain other actions’ sub-objects. So, you may have an actions.addToCounter(amount) or a sub-object with all counter actions called with actions.counter.add(amount).
The final version

The following file is the actual file in the NPM package use-global-hook.

function setState(newState) {
  this.state = { ...this.state, ...newState };
  this.listeners.forEach((listener) => {
    listener(this.state);
  });
}

function useCustom(React) {
  const newListener = React.useState()[1];
  React.useEffect(() => {
    this.listeners.push(newListener);
    return () => {
      this.listeners = this.listeners.filter(listener => listener !== newListener);
    };
  }, []);
  return [this.state, this.actions];
}

function associateActions(store, actions) {
  const associatedActions = {};
  Object.keys(actions).forEach((key) => {
    if (typeof actions[key] === 'function') {
      associatedActions[key] = actions[key].bind(null, store);
    }
    if (typeof actions[key] === 'object') {
      associatedActions[key] = associateActions(store, actions[key]);
    }
  });
  return associatedActions;
}

const useGlobalHook = (React, initialState, actions) => {
  const store = { state: initialState, listeners: [] };
  store.setState = setState.bind(store);
  store.actions = associateActions(store, actions);
  return useCustom.bind(store, React);
};

export default useGlobalHook;

Examples of use

You will never need to touch the useGlobalHook.js again. You may focus now on your application. Here are two examples of how to use it in real life.

Several counters, one value

Add as many counters as you want, it will all share the same global value. Every time one counter add 1 to the global value, all counters will render. The parent component won’t need to render again.

Click in “Open in Editor” to view the code in a new tab

Asynchronous ajax requests

Search GitHub repositories by username. Handle the ajax request asynchronously with async/await. Update the requests counter on every search.

Click in “Open in Editor” to view the code in a new tab

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JavaScript developers should you be using Web Workers?

JavaScript developers should you be using Web Workers?

Do you think JavaScript developers should be making more use of Web Workers to shift execution off of the main thread?

Originally published by David Gilbertson at https://medium.com

So, Web Workers. Those wonderful little critters that allow us to execute JavaScript off the main thread.

Also known as “no, you’re thinking of Service Workers”.

Photo by Caleb Jones on Unsplash

Before I get into the meat of the article, please sit for a lesson in how computers work:

Understood? Good.

For the red/green colourblind, let me explain. While a CPU is doing one thing, it can’t be doing another thing, which means you can’t sort a big array while a user scrolls the screen.

This is bad, if you have a big array and users with fingers.

Enter, Web Workers. These split open the atomic concept of a ‘CPU’ and allow us to think in terms of threads. We can use one thread to handle user-facing work like touch events and rendering the UI, and different threads to carry out all other work.

Check that out, the main thread is green the whole way through, ready to receive and respond to the gentle caress of a user.

You’re excited (I can tell), if we only have UI code on the main thread and all other code can go in a worker, things are going to be amazing (said the way Oprah would say it).

But cool your jets for just a moment, because websites are mostly about the UI — it’s why we have screens. And a lot of a user’s interactions with your site will be tapping on the screen, waiting for a response, reading, tapping, looking, reading, and so on.

So we can’t just say “here’s some JS that takes 20ms to run, chuck it on a thread”, we must think about where that execution time exists in the user’s world of tap, read, look, read, tap…

I like to boil this down to one specific question:

Is the user waiting anyway?

Imagine we have created some sort of git-repository-hosting website that shows all sorts of things about a repository. We have a cool feature called ‘issues’. A user can even click an ‘issues’ tab in our website to see a list of all issues relating to the repository. Groundbreaking!

When our users click this issues tab, the site is going to fetch the issue data, process it in some way — perhaps sort, or format dates, or work out which icon to show — then render the UI.

Inside the user’s computer, that’ll look exactly like this.

Look at that processing stage, locking up the main thread even though it has nothing to do with the UI! That’s terrible, in theory.

But think about what the human is actually doing at this point. They’re waiting for the common trio of network/process/render; just sittin’ around with less to do than the Bolivian Navy.

Because we care about our users, we show a loading indicator to let them know we’ve received their request and are working on it — putting the human in a ‘waiting’ state. Let’s add that to the diagram.

Now that we have a human in the picture, we can mix in a Web Worker and think about the impact it will have on their life:

Hmmm.

First thing to note is that we’re not doing anything in parallel. We need the data from the network before we process it, and we need to process the data before we can render the UI. The elapsed time doesn’t change.

(BTW, the time involved in moving data to a Web Worker and back is negligible: 1ms per 100 KB is a decent rule of thumb.)

So we can move work off the main thread and have a page that is responsive during that time, but to what end? If our user is sitting there looking at a spinner for 600ms, have we enriched their experience by having a responsive screen for the middle third?

No.

I’ve fudged these diagrams a little bit to make them the gorgeous specimens of graphic design that they are, but they’re not really to scale.

When responding to a user request, you’ll find that the network and DOM-manipulating part of any given task take much, much longer than the pure-JS data processing part.

I saw an article recently making the case that updating a Redux store was a good candidate for Web Workers because it’s not UI work (and non-UI work doesn’t belong on the main thread).

Chucking the data processing over to a worker thread sounds sensible, but the idea struck me as a little, umm, academic.

First, let’s split instances of ‘updating a store’ into two categories:

  1. Updating a store in response to a user interaction, then updating the UI in response to the data change
  2. Not that first one

If the first scenario, a user taps a button on the screen — perhaps to change the sort order of a list. The store updates, and this results in a re-rendering of the DOM (since that’s the point of a store).

Let me just delete one thing from the previous diagram:

In my experience, it is rare that the store-updating step goes beyond a few dozen milliseconds, and is generally followed by ten times that in DOM updating, layout, and paint. If I’ve got a site that’s taking longer than this, I’d be asking questions about why I have so much data in the browser and so much DOM, rather than on which thread I should do my processing.

So the question we’re faced with is the same one from above: the user tapped something on the screen, we’re going to work on that request for hopefully less than a second, why would we want to make the screen responsive during that time?

OK what about the second scenario, where a store update isn’t in response to a user interaction? Performing an auto-save, for example — there’s nothing more annoying than an app becoming unresponsive doing something you didn’t ask it to do.

Actually there’s heaps of things more annoying than that. Teens, for example.

Anyhoo, if you’re doing an auto-save and taking 100ms to process data client-side before sending it off to a server, then you should absolutely use a Web Worker.

In fact, any ‘background’ task that the user hasn’t asked for, or isn’t waiting for, is a good candidate for moving to a Web Worker.

The matter of value

Complexity is expensive, and implementing Web Workers ain’t cheap.

If you’re using a bundler — and you are — you’ll have a lot of reading to do, and probably npm packages to install. If you’ve got a create-react-app app, prepare to eject (and put aside two days twice a year to update 30 different packages when the next version of Babel/Redux/React/ESLint comes out).

Also, if you want to share anything fancier than plain data between a worker and the main thread you’ve got some more reading to do (comlink is your friend).

What I’m getting at is this: if the benefit is real, but minimal, then you’ve gotta ask if there’s something else you could spend a day or two on with a greater benefit to your users.

This thinking is true of everything, of course, but I’ve found that Web Workers have a particularly poor benefit-to-effort ratio.

Hey David, why you hate Web Workers so bad?

Good question.

This is a doweling jig:

I own a doweling jig. I love my doweling jig. If I need to drill a hole into the end of a piece of wood and ensure that it’s perfectly perpendicular to the surface, I use my doweling jig.

But I don’t use it to eat breakfast. For that I use a spoon.

Four years ago I was working on some fancy animations. They looked slick on a fast device, but janky on a slow one. So I wrote fireball-js, which executes a rudimentary performance benchmark on the user’s device and returns a score, allowing me to run my animations only on devices that would render them smoothly.

Where’s the best spot to run some CPU intensive code that the user didn’t request? On a different thread, of course. A Web Worker was the correct tool for the job.

Fast forward to 2019 and you’ll find me writing a routing algorithm for a mapping application. This requires parsing a big fat GeoJSON map into a collection of nodes and edges, to be used when a user asks for directions. The processing isn’t in response to a user request and the user isn’t waiting on it. And so, a Web Worker is the correct tool for the job.

It was only when doing this that it dawned on me: in the intervening quartet of years, I have seen exactly zero other instances where Web Workers would have improved the user experience.

Contrast this with a recent resurgence in Web Worker wonderment, and combine that contrast with the fact that I couldn’t think of anything else to write about, then concatenate that combined contrast with my contrarian character and you’ve got yourself a blog post telling you that maybe Web Workers are a teeny-tiny bit overhyped.

Thanks for reading

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Further reading

An Introduction to Web Workers

JavaScript Web Workers: A Beginner’s Guide

Using Web Workers to Real-time Processing

How to use Web Workers in Angular app

Using Web Workers with Angular CLI


Why ReactJS is better for Web Application Development?

Why ReactJS is better for Web Application Development?

Web Application Development is the point of contact for a business in today's digital era. It is important to choose the right platform for Web Application Development to build a high end Web

Web Application Development is essential for a business in today’s digital era. Finding the right platform for Web Application Development is important for building an effective Web Application that can enhance the overall customer engagement. Here’s what makes ReactJS a better option for building your next Web Application.