Tag: Expandable

Expandable Sections Within a CSS Grid

I love CSS Grid. I love how, with just a few lines of code, we can achieve fully responsive grid layouts, often without any media queries at all. I’m quite comfortable wrangling CSS Grid to produce interesting layouts, while keeping the HTML markup clean and simple.

But recently, I was presented with a unique UI conundrum to solve. Essentially, any given grid cell could have a button that would open up another, larger area that is also part of the grid. But this new larger grid cell needed to be:

  1. right below the cell that opened it, and
  2. full width.

Turns out there is a nice solution to it, and in the spirit of CSS Grid itself, it only involves a couple of lines of code. In this article, I’ll combine three one-line CSS Grid “tricks” to solve this. No JavaScript needed at all.

An explanation of the actual problem I need to solve

Here’s a minimalist UI example of what I needed to do:

This is our actual product card grid, as rendered in our Storybook component library:

A grid of product cards in a three by two layout. Each card has a placeholder gray image, product name, descriptions, price, and small text.

Each product card needed a new “quick view” button added such that, when clicked, it would:

  • dynamically “inject” a new full-width card (containing more detailed product information) immediately below the product card that was clicked,
  • without disrupting the existing card grid (i.e. retain the DOM source order and the visual order of the rendered cards in the browser), and
  • still be fully responsive.

Hmmm… was this even possible with our current CSS Grid implementation?

Surely I would need to resort to JavaScript to re-calculate the card positions, and move them around, especially on browser resize? Right?

Google was not my friend. I couldn’t find anything to help me. Even a search of “quick view” implementations only resulted in examples that used modals or overlays to render the injected card. After all, a modal is usually the only choice in situations like this, as it focuses the user on the new content, without needing to disrupt the rest of the page.

I slept on the problem, and ultimately came to a workable solution by combining some of CSS Grid’s most powerful and useful features.

CSS Grid Trick #1

I was already employing the first trick for our default grid system, and the product card grid is a specific instance of that approach. Here’s some (simplified) code:

.grid {   display: grid;   gap: 1rem;   grid-template-columns: repeat(auto-fit, 20rem); }

The “secret sauce” in this code is the grid-template-columns: repeat(auto-fit, 20rem); which gives us a grid with columns (20rem wide in this example) that are arranged automatically in the available space, wrapping to the next row when there’s not enough room.

Curious about auto-fit vs auto-fill? Sara Soueidan has written a wonderful explanation of how this works. Sara also explains how you can incorporate minmax() to enable the column widths to “flex” but, for the purposes of this article, I wanted to define fixed column widths for simplicity.

CSS Grid Trick #2

Next, I had to accommodate a new full-width card into the grid:

.fullwidth {   grid-column: 1 / -1; }

This code works because grid-template-columns in trick #1 creates an “explicit” grid, so it’s possible to define start and end columns for the .fullwidth card, where 1 / -1 means “start in column 1, and span every column up to the very last one.”

Great. A full-width card injected into the grid. But… now we have gaps above the full-width card.

Two rows of four rectangles. All of the rectangles are light gray and numbered, except one that has a wheat-colored background and another box beneath it containing text, and taking up the full container width.

CSS Grid Trick #3

Filling the gaps — I’ve done this before with a faux-masonry approach:

.grid {   grid-auto-flow: dense; }

That’s it! Required layout achieved.

The grid-auto-flow property controls how the CSS Grid auto-placement algorithm works. In this case, the dense packing algorithm tries to fills in holes earlier in the grid.

  • All our grid columns are the same width. Dense packing also works if the column widths are flexible, for example, by using minmax(20rem, 1f).
  • All our grid “cells” are the same height in each row. This is the default CSS Grid behavior. The grid container implicitly has align-items: stretch causing cells to occupy 100% of the available row height.

The result of all this is that the holes in our grid are filled — and the beautiful part is that the original source order is preserved in the rendered output. This is important from an accessibility perspective.

See MDN for a complete explanation of how CSS Grid auto-placement works.

The complete solution

These three combined tricks provide a simple layout solution that requires very little CSS. No media queries, and no JavaScript needed.

But… we do still need JavaScript?

Yes, we do. But not for any layout calculations. It is purely functional for managing the click events, focus state, injected card display, etc.

For demo purposes in the prototype, the full-width cards have been hard-coded in the HTML in their correct locations in the DOM, and the JavaScript simply toggles their display properties.

In a production environment, however, the injected card would probably be fetched with JavaScript and placed in the correct location. Grid layouts for something like products on an eCommerce site tend to have very heavy DOMs, and we want to avoid unnecessarily bloating the page weight further with lots of additional “hidden” content.

Quick views should be considered as a progressive enhancement, so if JavaScript fails to load, the user is simply taken to the appropriate product details page.

Accessibility considerations

I’m passionate about using correct semantic HTML markup, adding aria- properties when absolutely necessary, and ensuring the UI works with just a keyboard as well as in a screen reader.

So, here’s a rundown of the considerations that went into making this pattern as accessible as possible:

  • The product card grid uses a <ul><li> construct because we’re displaying a list of products. Assistive technologies (e.g. screen readers) will therefore understand that there’s a relationship between the cards, and users will be informed how many items are in the list.
  • The product cards themselves are <article> elements, with proper headings, etc.
  • The HTML source order is preserved for the cards when the .fullwidth card is injected, providing a good natural tab order into the injected content, and out again to the next card.
  • The whole card grid is wrapped in an aria-live region so that DOM changes are announced to screen readers.
  • Focus management ensures that the injected card receives keyboard focus, and on closing the card, keyboard focus is returned to the button that originally triggered the card’s visibility.

Although it isn’t demonstrated in the prototype, these additional enhancements could be added to any production implementation:

  • Ensure the injected card, when focused, has an appropriate label. This could be as simple as having a heading as the first element inside the content.
  • Bind the ESC key to close the injected card.
  • Scroll the browser window so that the injected card is fully visible inside the viewport.

Wrapping up

So, what do you think?

This could be a nice alternative to modals for when we want to reveal additional content, but without hijacking the entire viewport in the process. This might be interesting in other situations as well — think photo captions in an image grid, helper text, etc. It might even be an alternative to some cases where we’d normally reach for <details>/<summary> (as we know those are only best used in certain contexts).

Anyway, I’m interested in how you might use this, or even how you might approach it differently. Let me know in the comments!

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Performant Expandable Animations: Building Keyframes on the Fly

Animations have come a long way, continuously providing developers with better tools. CSS Animations, in particular, have defined the ground floor to solve the majority of uses cases. However, there are some animations that require a little bit more work.

You probably know that animations should run on the composite layer. (I won’t extend myself here, but if you want to know more, check this article.) That means animating transform or opacity properties that don’t trigger layout or paint layers. Animating properties like height and width is a big no-no, as they trigger those layers, which force the browser to recalculate styles.

On top of that, even when animating transform properties, if you want to truly hit 60 FPS animations, you probably should get a little help from JavaScript, using the FLIP technique for extra smoother animations! 

However, the problem of using transform for expandable animations is that the scale function isn’t exactly the same as animating width/height properties. It creates a skewed effect on the content, as all elements get stretched (when scaling up) or squeezed (when scaling down).

So, because of that, my go-to solution has been (and probably still is, for reasons I will detail later), technique #3 from Brandon Smith’s article. This still has a transition on height, but uses Javascript to calculate the content size, and force a transition using requestAnimationFrame. At OutSystems, we actually used this to build the animation for the OutSystems UI Accordion Pattern.

Generating keyframes with JavaScript

Recently, I stumbled on another great article from Paul Lewis, that details a new solution for expanding and collapsing animations, which motivated me to write this article and spread this technique around.

Using his words, the main idea consists of generating dynamic keyframes, stepping…

[…] from 0 to 100 and calculate what scale values would be needed for the element and its contents. These can then be boiled down to a string, which can be injected into the page as a style element. 

To achieve this, there are three main steps.

Step 1: Calculate the start and end states

We need to calculate the correct scale value for both states. That means we use getBoundingClientRect() on the element that will serve as a proxy for the start state, and divide it with the value from the end state. It should be something like this:

function calculateStartScale () {   const start= startElement.getBoundingClientRect();   const end= endElement.getBoundingClientRect();   return {     x: start.width / end.width,     y: start.height / end.height   }; }

Step 2: Generate the Keyframes

Now, we need to run a for loop, using the number of frames needed as the length. (It shouldn’t really be less than 60 to ensure a smooth animation.) Then, in each iteration, we calculate the correct easing value, using an ease function:

function ease (v, pow=4) {   return 1 - Math.pow(1 - v, pow); }  let easedStep = ease(i / frame);

With that value, we’ll get the scale of the element on the current step, using the following math:

const xScale = x + (1 - x) * easedStep; const yScale = y + (1 - y) * easedStep;

And then we add the step to the animation string:

animation += `$ {step}% {   transform: scale($ {xScale}, $ {yScale}); }`;

To avoid the content to get stretched/ skewed, we should perform a counter animation on it, using the inverted values:

const invXScale = 1 / xScale; const invYScale = 1 / yScale;  inverseAnimation += `$ {step}% {   transform: scale($ {invXScale}, $ {invYScale}); }`;

Finally, we can return the completed animations, or directly inject them in a newly created style tag.

Step 3: Enable the CSS animations 

On the CSS side of things, we need to enable the animations on the correct elements:

.element--expanded {   animation-name: animation;   animation-duration: 300ms;   animation-timing-function: step-end; }  .element-contents--expanded {   animation-name: inverseAnimation ;   animation-duration: 300ms;   animation-timing-function: step-end; }

You can check the example of a Menu from Paul Lewis article, on Codepen (courtesy of Chris Coyer):

Building an expandable section 

After grasping these baseline concepts, I wanted to check if I could apply this technique to a different use case, like a expandable section.

We only need to animate the height in this case, specifically on the function to calculate scales. We’re getting the Y value from the section title, to serve as the collapsed state, and the whole section to represent the expanded state:

    _calculateScales () {       var collapsed = this._sectionItemTitle.getBoundingClientRect();       var expanded = this._section.getBoundingClientRect();              // create css variable with collapsed height, to apply on the wrapper       this._sectionWrapper.style.setProperty('--title-height', collapsed.height + 'px');        this._collapsed = {         y: collapsed.height / expanded.height       }     }

Since we want the expanded section to have absolute positioning (in order to avoid it taking space when in a collapsed state), we are setting the CSS variable for it with the collapsed height, applied on the wrapper. That will be the only element with relative positioning.

Next comes the function to create the keyframes: _createEaseAnimations(). This doesn’t differ much from what was explained above. For this use case, we actually need to create four animations:

  1. The animation to expand the wrapper
  2. The counter-expand animation on the content
  3. The animation to collapse the wrapper
  4. The counter-collapse animation on the content

We follow the same approach as before, running a for loop with a length of 60 (to get a smooth 60 FPS animation), and create a keyframe percentage, based on the eased step. Then, we push it to the final animations strings:

outerAnimation.push(`   $ {percentage}% {     transform: scaleY($ {yScale});   }`);    innerAnimation.push(`   $ {percentage}% {     transform: scaleY($ {invScaleY});   }`);

We start by creating a style tag to hold the finished animations. As this is built as a constructor, to be able to easily add multiple patterns, we want to have all these generated animations on the same stylesheet. So, first, we validate if the element exists. If not, we create it and add a meaningful class name. Otherwise, you would end up with a stylesheet for each section expandable, which is not ideal.

 var sectionEase = document.querySelector('.section-animations');  if (!sectionEase) {   sectionEase = document.createElement('style');   sectionEase.classList.add('section-animations');  }

Speaking of that, you may already be wondering, “Hmm, if we have multiple expandable sections, wouldn’t they still be using the same-named animation, with possibly wrong values for their content?” 

You’re absolutely right! So, to prevent that, we are also generating dynamic animation names. Cool, right?

We make use of the index passed to the constructor from the for loop when making the querySelectorAll('.section') to add a unique element to the name:

var sectionExpandAnimationName = "sectionExpandAnimation" + index; var sectionExpandContentsAnimationName = "sectionExpandContentsAnimation" + index;

Then we use this name to set a CSS variable on the current expandable section. As this variable is only in this scope, we just need to set the animation to the new variable in the CSS, and each pattern will get its respective animation-name value.

.section.is--expanded {   animation-name: var(--sectionExpandAnimation); }  .is--expanded .section-item {   animation-name: var(--sectionExpandContentsAnimation); }  .section.is--collapsed {   animation-name: var(--sectionCollapseAnimation); }  .is--collapsed .section-item {   animation-name: var(--sectionCollapseContentsAnimation); }

The rest of the script is related to adding event listeners, functions to toggle the collapse/expand status and some accessibility improvements.

About the HTML and CSS: it needs a little bit of extra work to make the expandable functionality work. We need an extra wrapper to be the relative element that doesn’t animate. The expandable children have an absolute position so that they don’t occupy space when collapsed.

Remember, since we need to make counter animations, we make it scale full size in order to avoid a skew effect on the content.

.section-item-wrapper {   min-height: var(--title-height);   position: relative; }  .section {   animation-duration: 300ms;   animation-timing-function: step-end;   contain: content;   left: 0;   position: absolute;   top: 0;   transform-origin: top left;   will-change: transform; }  .section-item {   animation-duration: 300ms;   animation-timing-function: step-end;   contain: content;   transform-origin: top left;   will-change: transform;   }

I would like to highlight the importance of the animation-timing-functionproperty. It should be set to linear or step-end to avoid easing between each keyframe.

The will-change property — as you probably know — will enable GPU acceleration for the transform animation for an even smoother experience. And using the contains property, with a value of contents, will help the browser treat the element independently from the rest of the DOM tree, limiting the area before it recalculates the layout, style, paint and size properties.

We use visibility and opacity to hide the content, and stop screen readers to access it, when collapsed.

.section-item-content {   opacity: 1;   transition: opacity 500ms ease; }  .is--collapsed .section-item-content {   opacity: 0;   visibility: hidden; }

And finally, we have our section expandable! Here’s the complete code and demo for you to check:

Performance check

Anytime we work with animations, performance ought to be in the back of our mind. So, let’s use developer tools to check if all this work was worthy, performance-wise. Using the Performance tab (I’m using Chrome DevTools), we can analyze the FPS and the CPU usage, during the animations.

And the results are great!

The higher the green bar, the higher the frames. And there’s no junk either, which would be signed by red sections.

Using the FPS meter tool to check the values at greater detail, we can see that it constantly hits the 60 FPS mark, even with abusive usage.

Final considerations

So, what’s the verdict? Does this replace all other methods? Is this the “Holy Grail” solution?

In my opinion, no. 

But… that’s OK, really! It’s another solution on the list. And, as is true with any other method, it should be analyzed if it’s the best approach for the use-case.

This technique definitely has its merits. As Paul Lewis says, this does take a lot of work to prepare. But, on the flip side, we only need to do it once, when the page loads. During interactions, we are merely toggling classes (and attributes in some cases, for accessibility).

However, this brings some limitations for the UI of the elements. As you could see for the expandable section element, the counter-scale makes it much more reliable for absolute and off-canvas elements, like floating-actions or menus. It’s also difficult to styled borders because it’s using overflow: hidden.

Nevertheless, I think there’s tons of potential with this approach. Let me know what you think!

The post Performant Expandable Animations: Building Keyframes on the Fly appeared first on CSS-Tricks.


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