Skeleton Loading Pages with React

Skeleton Loading Pages with React

What are Skeleton pages? And how can you implement them in React?

What are Skeleton pages? And how can you implement them in React?

We’ve all been there.

You click a button expecting the next page to instantly fill your screen with content, only to be met with a dreaded loading icon — seconds become minutes as you frantically reload the page in a bid to get what you asked for.

My point being, nobody likes to wait…

In an aim to mitigate this torture emerged a clever visual illusion that seems to reduce the perceived loading time. Introducing **skeleton loading pages — **which are essentially a blank version of the page where information is gradually loaded.

Skeleton loading screens are widely used across pretty much all your favourite websites:

Facebook & YouTube

The user is instantly greeted with the skeleton as it pulses with grey shapes which mimic the page layout. The content requested replaces the placeholdersas they become available, until the skeleton’s job is done — creating the illusion of an instant transition.

Skeleton pages in React

There are some packages out there that you can use, for example React Loading Skeleton. However, this will add dependencies to your codebase and are not as customisable as if you were to develop your own. The rest of this guide will show you how to implement skeleton loading with styled-components, but the same principles can be applied with vanilla CSS.

The approach we went with for implementing skeleton loading pages is not to create a separate, dedicated skeleton page but rather a built-in ‘skeleton state’ of a component. This is a more robust and scalable solution that will allow for more flexible loading patterns across different pages.

Let’s start by making a simple skeleton component that can be reused across pages. First, let’s add some styling for the pulse of the skeleton. The reason we separate the pulse out, is so I can use it for more shapes (e.g. circles, rectangles, etc.) if needed.

const SSkeletonPulse = styled.div`
  display: inline-block;
  height: 100%;
  width: 100%;
  background: linear-gradient(-90deg, #F0F0F0 0%, #F8F8F8 50%, #F0F0F0 100%);
  background-size: 400% 400%;
  animation: pulse 1.2s ease-in-out infinite;
  @keyframes pulse {
    0% {
      background-position: 0% 0%;
    }
    100% {
      background-position: -135% 0%;
    }
  }
`;

Next, add some styling for the skeleton line. Skeleton components become more robust if they can inherit some styling from their parent element. A really effective trick is to use the line height of parent element to set the size of the skeleton component — this is done by using the ::before selector and filling it with empty content *(*a string, “\00a0”).

const SSkeletonLine = styled(SSkeletonPulse)`
  width: 5.5em;
  border-radius: 5px;

  &::before {
    content: "\00a0";
  }
`;

As you can see above, instead of having to create three skeleton lines with different sizes, the same skeleton line inherits three different sizes from the respective parent elements.

We can then export our skeleton line to be used across pages.

export const SkeletonLine = () => (
  <SSkeletonLine />
);

Now we have our skeleton, we need to implement it. As mentioned, the approach we use is to create a ‘skeleton state’ for the desired component. The implementation will depend on what data your page is using but we want the skeleton to render when the data we need is undefined and render the page once the data has been loaded. For example:

if (data === undefined) {
  const profileContent = (
    <Profile>
      <ProfileName><SkeletonLine /></ProfileName>
      <ProfileBio><SkeletonLine /></ProfileBio>
    </Profile>
  );
  } else {
    const profileContent = (
      <Profile>
        <ProfileName>{username}</ProfileName>
        <ProfileBio>{userBio}</ProfileBio>
      </Profile>
    );
}

return profileContent;

You could also use a ternary but I think it’s clearer to use if statements when components become more complex. This method allows you to import your skeleton to any component and it seamlessly build entire skeleton pages quickly.

If you want to build a more customisable skeleton, you can allow it to take in props that change the styling of the skeleton. For example, these skeletons work well on white/neutral backgrounds but not so well when the background is darker. I want to be able to make my skeleton line translucent for some pages:

const SSkeletonPulse = styled.div`
  display: inline-block;
  height: 100%;
  width: 100%;
  background: ${props =>
    props.translucent
      ? css`linear-gradient(-90deg, #C1C1C1 0%, #F8F8F8 50%, #C1C1C1 100%)`
      : css`linear-gradient(-90deg, #F0F0F0 0%, #F8F8F8 50%, #F0F0F0 100%)`};
  background-size: 400% 400%;
  animation: pulse 1.2s ease-in-out infinite;
  @keyframes pulse {
    0% {
      background-position: 0% 0%;
    }
    100% {
      background-position: -135% 0%;
    }
  }
`;

export const SkeletonLine = () => (
  <SSkeletonLine translucent={translucent} />
);

So, if I want to make the skeleton line translucent, all I have to do in the SkeletonLine element is:

<SkeletonLine translucent={true} />

Conclusion

Skeleton loading pages have become the go-to solution for all your loading transition needs. Some research validates the idea that the perceived loading time is shorter for skeletons as opposed to spinners, for example. But before you dive in to skeletons, there are some caveats:

You are increasing the amount of code you have — your components will need an additional layer of logic to handle what should be rendered and when. This will add a significant amount of code to what was originally a simple React component and could make things harder to debug. Also, as mentioned above, if you decide to use a package, you are adding more dependencies to your codebase, which increases security risks and is less customisable than implementing a simple solution yourself.

Changes to components inevitably mean changes to the skeleton. The method outlined above is robust, however, if you change the layout or add features, you also need to make sure the skeletons are changed to reflect that.

Although some research validates skeleton loading pages, there has also been skepticism around their effectiveness; citing small sample size and lack of variation as concerns about studies conducted — there have even been conflicting reports stating that skeleton pages may perform worse for perceived loading time.

Regardless, the use of skeleton loading pages is everywhere and is quickly becoming the expectation of what the ‘loading experience’ is. As you can see, it’s not hard to do, so give it a go, experiment with different approaches and decide if they are just a trend or if they really do work…

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