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Testing for front end category

Adebola Adesina

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Test Post

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"One of Jhey’s main mantras is to make learning fun. In this article, he shows you ways to level up your skills by bringing your ideas to life, and not forgetting that you can be playful with code. With that mindset, every idea is bound to become an opportunity to try something new." – Vitaly Friedman

Naming things is hard, right? "Flippy Snaps" was the best thing I could come up with 😂 I saw an effect like this on TV one evening and made a note to myself to make something similar. Although this isn't something I'd look to drop on a website any time soon, it's a neat little challenge to make. It fits in with my whole stance on "Playfulness in Code" to learn. Anyway, a few days later, I sat down at the keyboard, and a couple of hours later I had this.

My final demo is a React app, but we don't need to dig into using React to explain the mechanics of making this work. We will create the React app once we’ve established how to make things work.

Audio

Oh. And here's an unordered list:

And how about numbered lists:

  1. Cool thing
  2. Awesome thing
  3. Nice thing
  4. Ended things

Check lists?

Let's start by creating a grid. Let's say we want a 10 by 10 grid. That's 100 cells (This is why React is handy for something like this). Each cell is going to consist of an element that contains the front and back for a flippable card.

<div class="flippy-snap">
  <!-- 100 of these -->
  <div class="flippy-snap__card flippy-card">
    <div class="flippy-card__front"></div>
    <div class="flippy-card__rear"></div>
  </div>
</div>

The styles for our grid are quite straightforward. We can use display: grid and use a custom property for the grid size. Here we are defaulting to 10.

console.info(true === true)
.flippy-snap {
  display: grid;
  grid-gap: 1px;
  grid-template-columns: repeat(var(--grid-size, 10), 1fr);
  grid-template-rows: repeat(var(--grid-size, 10), 1fr);
}

We won’t use grid-gap in the final demo, but, it’s good for seeing the cells easier whilst developing.

Next, we need to style the sides to our cards and display images. We can do this by leveraging inline CSS custom properties. Let's start by updating the markup. We need each card to know its x and y position in the grid.

<div class="flippy-snap">
  <div class="flippy-snap__card flippy-card" style="--x: 0; --y: 0;">
    <div class="flippy-card__front"></div>
    <div class="flippy-card__rear"></div>
  </div>
  <div class="flippy-snap__card flippy-card" style="--x: 1; --y: 0;">
    <div class="flippy-card__front"></div>
    <div class="flippy-card__rear"></div>
  </div>
  <!-- Other cards -->
</div>

For the demo, I'm using Pug to generate this for me. You can see the compiled HTML by clicking “View Compiled HTML” in the demo.

- const GRID_SIZE = 10
- const COUNT = Math.pow(GRID_SIZE, 2)
.flippy-snap
  - for(let f = 0; f < COUNT; f++)
    - const x = f % GRID_SIZE
    - const y = Math.floor(f / GRID_SIZE)
    .flippy-snap__card.flippy-card(style=`--x: ${x}; --y: ${y};`)
      .flippy-card__front
      .flippy-card__rear

Then we need some styles.

.flippy-card {
  --current-image: url("https://random-image.com/768");
  --next-image: url("https://random-image.com/124");
  height: 100%;
  width: 100%;
  position: relative;
}
.flippy-card__front,
.flippy-card__rear {
  position: absolute;
  height: 100%;
  width: 100%;
  backface-visibility: hidden;
  background-image: var(--current-image);
  background-position: calc(var(--x, 0) * -100%) calc(var(--y, 0) * -100%);
  background-size: calc(var(--grid-size, 10) * 100%);
}
.flippy-card__rear {
  background-image: var(--next-image);
  transform: rotateY(180deg) rotate(180deg);
}

The rear of the card gets its position using a combination of rotations via transform. But, the interesting part is how we show the image part for each card. In this demo, we are using a custom property to define the URLs for two images. And then we set those as the background-image for each card face. But the trick is how we define the background-size and background-position. Using the custom properties --x and --y we multiply the value by -100%. And then we set the background-size to --grid-size multiplied by 100%. This gives displays the correct part of the image for a given card.

You may have noticed that we had --current-image and --next-image. But, currently, there is no way to see the next image. For that, we need a way to flip our cards. We can use another custom property for this. Let's introduce a --count property and set a transform for our cards.

.flippy-snap {
  --count: 0;
  perspective: 50vmin;
}
.flippy-card {
  transform: rotateX(calc(var(--count) * -180deg));
  transition: transform 0.25s;
  transform-style: preserve-3d;
}

We can set the --count property on the containing element. Scoping means all the cards can pick up that value and use it to transform their rotation on the x-axis. We also need to set transform-style: preserve-3d so that we see the back of the cards. Setting a perspective gives us that 3D perspective.

This demo lets you update the --count property value so you can see the effect it has.

What next?

At this point, you could wrap it up there and set a simple click handler that increments --count by one on each click.

const SNAP = document.querySelector('.flippy-snap')
let count = 0
const UPDATE = () => SNAP.style.setProperty('--count', count++)
SNAP.addEventListener('click', UPDATE)

Remove the grid-gap and you'd get this. Click the snap to flip it.

Now we have the basic mechanics worked out, it's time to turn this into a React app. There's a bit to break down here.

const App = () => {
  const [snaps, setSnaps] = useState([])
  const [disabled, setDisabled] = useState(true)
  const [gridSize, setGridSize] = useState(9)
  const snapRef = useRef(null)

  const grabPic = async () => {
    const pic = await fetch('https://source.unsplash.com/random/1000x1000')
    return pic.url
  }

  useEffect(() => {
    const setup = async () => {
      const url = await grabPic()
      const nextUrl = await grabPic()
      setSnaps([url, nextUrl])
      setDisabled(false)
    }
    setup()
  }, [])

  const setNewImage = async count => {
    const newSnap = await grabPic()
    setSnaps(
      count.current % 2 !== 0 ? [newSnap, snaps[1]] : [snaps[0], newSnap]
    )
    setDisabled(false)
  }

  const onFlip = async count => {
    setDisabled(true)
    setNewImage(count)
  }

  if (snaps.length !== 2) return <h1 className="loader">Loading...</h1>

  return (
    <FlippySnap
      gridSize={gridSize}
      disabled={disabled}
      snaps={snaps}
      onFlip={onFlip}
      snapRef={snapRef}
    />
  )
}

Our App component handles grabbing images and passing them to our FlippySnap component. That's the bulk of what's happening here. For this demo, we're grabbing images from Unsplash.

const grabPic = async () => {
  const pic = await fetch('https://source.unsplash.com/random/1000x1000')
  return pic.url
}

// Initial effect grabs two snaps to be used by FlippySnap
useEffect(() => {
  const setup = async () => {
    const url = await grabPic()
    const nextUrl = await grabPic()
    setSnaps([url, nextUrl])
    setDisabled(false)
  }
  setup()
}, [])

Cool Beans

If there aren't two snaps to show, then we show a "Loading..." message.

if (snaps.length !== 2) return <h1 className="loader">Loading...</h1>

If we are grabbing a new image, we need to disable FlippySnap so we can't spam click it.

<FlippySnap
  gridSize={gridSize}
  disabled={disabled} // Toggle a "disabled" prop to stop spam clicks
  snaps={snaps}
  onFlip={onFlip}
  snapRef={snapRef}
/>

We're letting App dictate the snaps that get displayed by FlippySnap and in which order. On each flip, we grab a new image, and depending on how many times we've flipped, we set the correct snaps. The alternative would be to set the snaps and let the component figure out the order.

const setNewImage = async count => {
  const newSnap = await grabPic() // Grab the snap
  setSnaps(
    count.current % 2 !== 0 ? [newSnap, snaps[1]] : [snaps[0], newSnap]
  ) // Set the snaps based on the current "count" which we get from FlippySnap
  setDisabled(false) // Enable clicks again
}

const onFlip = async count => {
  setDisabled(true) // Disable so we can't spam click
  setNewImage(count) // Grab a new snap to display
}

Beanies

How might FlippySnap look? There isn’t much to it at all!

const FlippySnap = ({ disabled, gridSize, onFlip, snaps }) => {
  const CELL_COUNT = Math.pow(gridSize, 2)
  const count = useRef(0)

  const flip = e => {
    if (disabled) return
    count.current = count.current + 1
    if (onFlip) onFlip(count)
  }

  const buttonStyle = {
    "--grid-size": gridSize,
    "--count": count.current,
    "--current-image": `url('${snaps[0]}')`,
    "--next-image": `url('${snaps[1]}')`,
  }

  return (
    <button
      className="flippy-snap"
      ref={containerRef}
      style={buttonStyle}>
      {new Array(CELL_COUNT).fill().map((cell, index) => {
        const x = index % gridSize
        const y = Math.floor(index / gridSize)
        const cellStyle = {
          "--x": x,
          "--y": y,
        }
        return (
          <span
            key={index}
            className="flippy-card"
            style={cellStyle}>
            <span className="flippy-card__front"></span>
            <span className="flippy-card__rear"></span>
          </span>
        )
      }}
    </button>
  )
}

The component handles rendering all the cards and setting the inline custom properties. The onClick handler for the container increments the count. It also triggers the onFlip callback. If the state is currently disabled, it does nothing. That flip of the disabled state and grabbing a new snap triggers the flip when the component re-renders.

We have a React component that will now flip through images for as long as we want to keep requesting new ones. But, that flip transition is a bit boring. To spice it up, we're going to make use of GreenSock and it's utilities. In particular, the "distribute" utility. This will allow us to distribute the delay of flipping our cards in a grid like burst from wherever we click. To do this, we're going to use GreenSock to animate the --count value on each card.

It's worth noting that we have a choice here. We could opt to apply the styles with GreenSock. Instead of animating the --count property value, we could animate rotateX. We could do this based on the count ref we have. And this also goes for any other things we choose to animate with GreenSock in this article. It's down to preference and use case. You may feel that updating the custom property value makes sense. The benefit being that you don't need to update any JavaScript to get a different styled behavior. We could change the CSS to use rotateY for example.

Our updated flip function could look like this:

const flip = e => {
  if (disabled) return
  const x = parseInt(e.target.parentNode.getAttribute('data-snap-x'), 10)
  const y = parseInt(e.target.parentNode.getAttribute('data-snap-y'), 10)
  count.current = count.current + 1
  gsap.to(containerRef.current.querySelectorAll('.flippy-card'), {
    '--count': count.current,
    delay: gsap.utils.distribute({
      from: [x / gridSize, y / gridSize],
      amount: gridSize / 20,
      base: 0,
      grid: [gridSize, gridSize],
      ease: 'power1.inOut',
    }),
    duration: 0.2,
    onComplete: () => {
      // At this point update the images
      if (onFlip) onFlip(count)
    },
  })
}

Note how we're getting an x and y value by reading attributes of the clicked card. For this demo, we've opted for adding some data attributes to each card. These attributes communicate a cards position in the grid. We’re also using a new ref called containerRef. This is so we reference only the cards for a FlippySnap instance when using GreenSock.

{new Array(CELL_COUNT).fill().map((cell, index) => {
  const x = index % gridSize
  const y = Math.floor(index / gridSize)
  const cellStyle = {
    "--x": x,
    "--y": y,
  }
  return (
    <span
      className="flippy-card"
      data-snap-x={x}
      data-snap-y={y}
      style={cellStyle}>
      <span className="flippy-card__front"></span>
      <span className="flippy-card__rear"></span>
    </span>
  )
})}

Once we get those x and y values, we can make use of them in our animation. Using gsap.to we want to animate the --count custom property for every .flippy-card that's a child of containerRef.

To distribute the delay from where we click, we set the value of delay to use gsap.utils.distribute. The from value of the distribute function takes an Array containing ratios along the x and y axis. To get this, we divide x and y by gridSize. The base value is the initial value. For this, we want 0 delay on the card we click. The amount is the largest value. We've gone for gridSize / 20 but you could experiment with different values. Something based on the gridSize is a good idea though. The grid value tells GreenSock the grid size to use when calculating distribution. Last but not least, the ease defines the ease of the delay distribution.

gsap.to(containerRef.current.querySelectorAll('.flippy-card'), {
  '--count': count.current,
  delay: gsap.utils.distribute({
    from: [x / gridSize, y / gridSize],
    amount: gridSize / 20,
    base: 0,
    grid: [gridSize, gridSize],
    ease: 'power1.inOut',
  }),
  duration: 0.2,
  onComplete: () => {
    // At this point update the images
    if (onFlip) onFlip(count)
  },
})

As for the rest of the animation, we are using a flip duration of 0.2 seconds. And we make use of onComplete to invoke our callback. We pass the flip count to the callback so it can use this to determine snap order. Things like the duration of the flip could get configured by passing in different props if we wished.

Putting it all together gives us this:

Those that like to push things a bit might have noticed that we can still "spam" click the snap. And that's because we don't disable FlippySnap until GreenSock has completed. To fix this, we can use an internal ref that we toggle at the start and end of using GreenSock.

const flipping = useRef(false) // New ref to track the flipping state

const flip = e => {
  if (disabled || flipping.current) return
  const x = parseInt(e.target.parentNode.getAttribute('data-snap-x'), 10)
  const y = parseInt(e.target.parentNode.getAttribute('data-snap-y'), 10)
  count.current = count.current + 1
  gsap.to(containerRef.current.querySelectorAll('.flippy-card'), {
    '--count': count.current,
    delay: gsap.utils.distribute({
      from: [x / gridSize, y / gridSize],
      amount: gridSize / 20,
      base: 0,
      grid: [gridSize, gridSize],
      ease: 'power1.inOut',
    }),
    duration: 0.2,
    onStart: () => {
      flipping.current = true
    },
    onComplete: () => {
      // At this point update the images
      flipping.current = false
      if (onFlip) onFlip(count)
    },
  })
}

And now we can no longer spam click our FlippySnap!

Now it's time for some extra touches. At the moment, there's no visual sign that we can click our FlippySnap. What if when we hover, the cards raise towards us? We could use onPointerOver and use the "distribute" utility again.

const indicate = e => {
  const x = parseInt(e.currentTarget.getAttribute('data-snap-x'), 10)
  const y = parseInt(e.currentTarget.getAttribute('data-snap-y'), 10)
  gsap.to(containerRef.current.querySelectorAll('.flippy-card'), {
    '--hovered': gsap.utils.distribute({
      from: [x / gridSize, y / gridSize],
      base: 0,
      amount: 1,
      grid: [gridSize, gridSize],
      ease: 'power1.inOut'
    }),
    duration: 0.1,
  })
}

Here, we are setting a new custom property on each card named --hovered. This is set to a value from 0 to 1. Then within our CSS, we are going to update our card styles to watch for the value.

.flippy-card {
  transform: translate3d(0, 0, calc((1 - (var(--hovered, 1))) * 5vmin))
              rotateX(calc(var(--count) * -180deg));
}

Here we are saying a card will move on the z-axis at most 5vmin.

We then apply this to each card using the onPointerOver prop.

{new Array(CELL_COUNT).fill().map((cell, index) => {
  const x = index % gridSize
  const y = Math.floor(index / gridSize)
  const cellStyle = {
    "--x": x,
    "--y": y,
  }
  return (
    <span
      onPointerOver={indicate}
      className="flippy-card"
      data-snap-x={x}
      data-snap-y={y}
      style={cellStyle}>
      <span className="flippy-card__front"></span>
      <span className="flippy-card__rear"></span>
    </span>
  )
})}

And when our pointer leaves our FlippySnap we want to reset our card positions.

const reset = () => {
  gsap.to(containerRef.current.querySelectorAll('.flippy-card'), {
    '--hovered': 1,
    duration: 0.1,
  })
}

And we can apply this with the onPointerLeave prop.

<button
  className="flippy-snap"
  ref={containerRef}
  onPointerLeave={reset}
  style={buttonStyle}
  onClick={flip}>

Put that all together and we get something like this. Try moving your pointer over it.

What next? How about a loading indicator so we know when we our App is grabbing the next image? We can render a loading spinner when our FlippySnap is disabled.

{disabled && <span className='flippy-snap__loader'></span>}

The styles for which could make a rotating circle.

.flippy-snap__loader {
  border-radius: 50%;
  border: 6px solid #fff;
  border-left-color: #000;
  border-right-color: #000;
  position: absolute;
  right: 10%;
  bottom: 10%;
  height: 8%;
  width: 8%;
  transform: translate3d(0, 0, 5vmin) rotate(0deg);
  animation: spin 1s infinite;
}
@keyframes spin {
  to {
    transform: translate3d(0, 0, 5vmin) rotate(360deg);
  }
}

And this gives us a loading indicator when grabbing a new image.

That's it!

That's how we can create a FlippySnap with React and GreenSock. It's fun to make things that we may not create on a day to day basis. Demos like this can pose different challenges and can level up your problem solving game.

I took it a little further and added a slight parallax effect along with some audio. You can also configure the grid size! Big grids affect performance though. It’s also worth noting that this demo works best in Chromium based browsers. Where would you take it next? I'd like to see if I can recreate it with ThreeJS next. That’ll address the performance 😅

Stay Awesome! ʕ •ᴥ•ʔ

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