Michelle Barker appears as one of a heavenly host, coming forth with scroll in hand to pronounce an end to janky scrolljacking! Unto us a new specification is born, in the city of TimBL, and its name shall be called Scroll Snap.

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One area where the web has traditionally lagged behind native platforms is the perceived “slickness” of the app experience. In part, this perception comes from the way the UI responds to user interactions – including the act of scrolling through content.

Faced with the limitations of the web platform, developers frequently reach for JavaScript libraries and frameworks to alter the experience of scrolling a web page – sometimes called “scroll-jacking” – not always a good thing if implemented without due consideration of the user experience. More libraries can also lead to page bloat, and drag down a site’s performance. But with the relatively new CSS Scroll Snap specification, we have the ability to control the scrolling behaviour of a web page (to a degree) using web standards – without resorting to heavy libraries. Let’s take a look at how.

Scroll Snap

A user can control the scroll position of a web page in a number of ways, such as using a mouse, touch gesture or arrow keys. In contrast to a linear scrolling experience, where the rate of scroll reflects the rate of the controller, the Scroll Snap specification enables a web page to snap to specific points as the user scrolls. For this, we need a fixed-height element to act as the scroll container, and the direct children of that element will determine the snap points. To demonstrate this, here is some example HTML, which consists of a <div> containing four <section> elements:

<div class="scroll-container">
  <section>
    <h2>Section 1</h2>
  </section>
  <section>
    <h2>Section 2</h2>
  </section>
  <section>
    <h2>Section 3</h2>
  </section>
  <section>
    <h2>Section 4</h2>
  </section>
</div>

Scroll snapping requires the presence of two main CSS properties: scroll-snap-type and scroll-snap-align. scroll-snap-type applies to the scroll container element, and takes two keyword values. It tells the browser:

• The direction to snap
• Whether snapping is mandatory

scroll-snap-align is applied to the child elements – in this case our <section>s.

We also need to set a fixed height on the scroll container, and set the relevant overflow property to scroll.

.scroll-container {
  height: 100vh;
  overflow-y: scroll;
  scroll-snap-type: y mandatory;
}

section {
  height: 100vh;
  scroll-snap-align: center;
}

In the above example, I’m setting the direction in the scroll-snap-type property to y to specify vertical snapping. The second value specifies that snapping is mandatory. This means that when the user stops scrolling their scroll position will always snap to the nearest snap point. The alternative value is proximity, which determines that the user’s scroll position will be snapped only if they stop scrolling in the proximity of a snap point. (It’s down to the browser to determine what it considers to be the proximity threshold.)

If you have content of indeterminate length, which might feasibly be larger than the height of the scroll container (in this case 100vh), then using a value of mandatory can cause some content to be hidden above or below the visible area, so is not recommended. But if you know that your content will always fit within the viewport, then mandatory can produce a more consistent user experience.

In this example I’m setting both the scroll container and each of the sections to a height of 100vh, which affects the scroll experience of the entire web page. But scroll snapping can also be implemented on smaller components too. Setting scroll snapping on the x-axis (or inline axis) can produce something like a carousel effect.

In this demo, you can scroll horizontally scroll through the sections:

The Intersection Observer API

By implementing the CSS above, our web page already has a more native-like feel to it. To improve upon this further we could add some scroll-based transitions and animations. We’ll need to employ a bit of Javascript for this, using the Intersection Observer API. This allows us to create an observer that watches for elements intersecting with the viewport, triggering a callback function when this occurs. It is more efficient than libraries that rely on continuously listening for scroll events.

We can create an observer that watches for each of our scroll sections coming in and out of view:

const sections = [...document.querySelectorAll('section')]

const options = {
  rootMargin: '0px',
  threshold: 0.25
}

const callback = (entries) => {
  entries.forEach((entry) => {
    if (entry.intersectionRatio >= 0.25) {
      target.classList.add("is-visible");
    } else {
      target.classList.remove("is-visible");
    }
  })
}

const observer = new IntersectionObserver(callback, options)

sections.forEach((section, index) => {
  observer.observe(section)
})

In this example, a callback function is triggered whenever one of our sections intersects the container by 25% (using the threshold option). The callback adds a class of is-visible to the section if it is at least 25% in view when the intersection occurs (which will take effect when the element is coming into view), and removes it otherwise (when the element is moving out of view). Then we can add some CSS to transition in the content for each of those sections:

section .content {
  opacity: 0:
}

section.is-visible .content {
  opacity: 1;
  transition: opacity 1000ms:
}

This demo shows it in action:

You could, of course, implement some much more fancy transition and animation effects in CSS or JS!

As an aside, it’s worth pointing out that, in practice, we shouldn’t be setting opacity: 0 as the default without considering the experience if JavaScript fails to load. In this case, the user would see no content at all! There are different ways to handle this: We could add a .no-js class to the body (which we remove on load with JS), and set default styles on it, or we could set the initial style (before transition) with JS instead of CSS.

Position: sticky

There’s one more CSS property that I think has the potential to aid the scroll experience, and that’s the position property. Unlike position: fixed, which locks the position of an element relative to the nearest relative ancestor and doesn’t change, position: sticky is more like a temporary lock. An element with a position value of sticky will become fixed only until it reaches the threshold of its parent, at which point it resumes relative positioning.

By “sticking” some elements within scroll sections we can give the impression of them being tied to the action of scrolling between sections. It’s pretty cool that we can instruct an element to respond to it’s position within a container with CSS alone!

Browser support and fallbacks

The scroll-snap-type and scroll-snap-align properties are fairly well-supported. The former requires a prefix for Edge and IE, and older versions of Safari do not support axis values. In newer versions of Safari it works quite well. Intersection Observer similarly has a good level of support, with the exception of IE.

By wrapping our scroll-related code in a feature query we can provide a regular scrolling experience as a fallback for users of older browsers, where accessing the content is most important. Browsers that do not support scroll-snap-type with an axis value would simply scroll as normal.

@supports (scroll-snap-type: y mandatory) {
  .scroll-container {
    height: 100vh;
    overflow-y: scroll;
    scroll-snap-type: y mandatory;
  }

  section {
    height: 100vh;
    scroll-snap-align: center;
  }
}

The above code would exclude MS Edge and IE, as they don’t support axis values. If you wanted to support them you could do so using a vendor prefix, and using @supports (scroll-snap-type: mandatory) instead.

Putting it all together

This demo combines all three of the effects discussed in this article.

Summary

Spending time on scroll-based styling might seem silly or frivolous to some. But I believe it’s an important part of positioning the web as a viable alternative to native applications, keeping it open and accessible. While these new CSS features don’t offer all of the control we might expect with a fully featured JS library, they have a major advantage: simplicity and reliability. By utilising web standards where possible, we can have the best of both worlds: Slick and eye-catching sites that satisfy clients’ expectations, with the added benefit of better performance for users.

About the author

Michelle is a Lead Front End Developer at Bristol web agency Atomic Smash, author of front-end blog CSS { In Real Life }, and a Mozilla Tech Speaker. She has written articles for CSS Tricks, Smashing Magazine, and Web Designer Magazine, to name a few. She enjoys experimenting with new CSS features and helping others learn about them.

More articles by Michelle

Colin Bendell gets into the minutia of microbrowsers - the small previews of your site that are pervasive all around the web and through social media apps and search engines whenever an item of content on your site is referenced.

You’ve seen it everywhere - that little thumbnail preview of a website mentioned in a tweet, the expanded description in a Slack channel, or in WhatsApp group chat.

Figure 1: The preview shown in a group chat provides a hint of what the real webpage looks like

These link previews are so commonplace that we hardly pay any attention to how our site design might be impacting the generated preview. Yet, these previews can be the most influential part for attracting new audiences and increasing engagement - possibly more than SEO. Even more alarming is that most web analytics are blind to this traffic and can’t show you how these Microbrowsers are interacting with your site.

As we close out the year, here are five essential questions and ideas that every web dev should know about Microbrowsers.

1. What are Microbrowsers? How are they different from “normal” browser?

We are all very familiar with the main browsers like Firefox, Safari, Chrome, Edge and Internet Explorer. Not to mention the many new browsers that use Chromium as the rendering engine but offer unique user experiences like Samsung Internet or Brave.

In contrast, Microbrowsers are a class of User-Agents that also visit website links, parse HTML and generate a user experience. But unlike those traditional browsers, the HTML parsing is limited and the rendering engine is singularly focused. The experience is not intended to be interactive. Rather the experience is intended to be representational - to give the user a hint of what exists on the other side of the URL.

Creating link previews is not new. Facebook and Twitter have been adding these link previews in posts for nearly a decade. That used to be the primary use case. Marketing teams created backlog items to adopt different microdata - from Twitter Cards and Open Graph annotations for Facebook. LinkedIn likewise embraced both Open Graph and OEmbed tags to help generate the previews

<meta name="description" content="seo description long">
<meta name="keywords" content="seo keyword list">

<link rel="shortcut icon" href="favicon.ico" 
                          type="image/x-icon">
<link rel="icon" href="favicon_32.png" sizes="32x32">
<link rel="icon" href="favicon_48.png" sizes="48x48">
<link rel="icon" href="favicon_96.png" sizes="96x96">
<link rel="icon" href="favicon_144.png" sizes="144x144">

<meta property="og:title" content="Short title here" />
<meta property="og:description" content="shortish description" />
<meta name="twitter:title" content="Short title here">
<meta name="twitter:description" content="shortish description">

<meta property="og:image"
      content="https://res.cloudinary.com/.../hero-img.png" />

<meta name="twitter:image:src"
      content="https://res.cloudinary.com/.../hero-img.png">

As group chats and other collaboration tools have become more prevalent, we have seen many features from the big social media platforms emerge. Particularly in recent years we’ve seen the adoption of the link unfurling behaviour in these chat platforms. Rather than reinventing the wheel, each platform looks for pre-existing microdata to generate the preview.

But which data should be used? How should this be arranged? As it turns out, each platform behaves slightly differently; presenting information in slightly different ways.

Figure 2: The same amazon link shared in iMessage (left), Hangouts and WhatsApp (right)

2. If Microbrowsers are everywhere, why don’t I see them in my analytics reports?

It’s easy to miss the traffic from Microbrowsers. This is for a number of reasons:

First, page requests from Microbrowsers don’t run JavaScript and they don’t accept cookies. The Google Analytics <script> block won’t be run or executed. And all cookie will be ignored by the rendering agent.

Second, if you were to do a log analysis based on HTTP logs from your CDN or web stack, you would see a relatively small volume of traffic. That is assuming you can identify the User-Agent strings. Some of these Microbrowsers impersonate real browsers and others impersonate Facebook or twitter. For example, iMessage uses the same User-Agent string for all these requests and it hasn’t changed since iOS 9.

User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_1) 
             AppleWebKit/601.2.4 (KHTML, like Gecko) 
             Version/9.0.1 Safari/601.2.4 
             facebookexternalhit/1.1  
             Facebot Twitterbot/1.0

Finally, many platforms - particularly Facebook Messenger and Hangouts use centralized services to request the preview layout. This, in contrast to WhatsApp and iMessage where you will see one request per user. In the centralized consumer approach your web servers will only see one request, but this one request might represent thousands of eyeballs.

3. Microbrowser are probably more important than google bot

We all know the importance of having our web sites crawled by search engines like googlebot. These bots are the lifeblood for lead generation and for discovering new users.

However, the real gold for marketers is from word-of-mouth discussions. Those conversations with your friends when you recommend a TV show, a brand of clothing, or share a news report. This is the most valuable kind of marketing.

Last year when assembling the data for Cloudinary’s State of the Visual Media report, I discovered that there was a very prominent usage pattern over the USA holiday season. During thanksgiving, all the way to Black Friday, the rate of link sharing skyrocketed as group chats shared deals and insights.

Zooming out (and normalizing for time-of-day), we can see that there is a daily cadence of link sharing and word of mouth referrals. It probably isn’t a shock to see that we predominantly share links in Slack between Monday and Friday, while WhatsApp is used all week long. Likewise, WhatsApp is most often used during our ‘break’ times like lunch or in the evening after we put the kids to bed.

While the link preview is increasingly common, there are two user behaviours to balance:

• Users can be skeptical of links sent via SMS and other chats. We don’t want to be fooled into clicking a phishing links and so we look for other queues to offer validation. This is why most platforms use the preview while also emphasize the website url host name.

• Skimming. I’m sure you’ve had the experience coming out of a meeting or grocery store to find a group chat with 100 messages. As you scroll to catch up on the conversation, links can easily be skipped. In this way, users expect the preview to act as a summary to tell them how important it is to visit the link.

Figure 4: Nielsen Norman Group summarizes the research in a dynamic image preview

Figure 5: A mockup of how an ecommerce product could create compelling previews showcasing colors, stock and price in the preview

4. Microbrowsers are not real browsers (they just play one on TV)

As I previously mentioned, Microbrowsers pretend to be a browser in that they send the right HTTP headers and often send impersonating User-Agent strings. Yet, there are several characteristics that a web dev should be aware of.

First, Microbrowsers try to protect the User’s privacy. The user hasn’t decided to visit your site yet, and more importantly, the user is having a private conversation. The fact that your brand or website is mentioned should just make your ears burn, but you shouldn’t be able to listen in to the conversation.

For this reason, all Microbrowsers:

• don’t execute JavaScript - so your react application won’t work
• ignore all cookies - so your A/B or red/green cookies will be ignored
• some will follow redirects, but will quickly time out after a few seconds and give up trying to expand the link.
• there won’t be a referer: HTTP header when the user clicks the link for the full browser. In fact, a new user will appear as ‘direct’ traffic - as though they typed in the url.

Second, Microbrowsers have a very small brain and very likely don’t use an advanced network algorithm. Most browsers will use a tokenizer to parse the HTML markup and send requests to the network stack asynchronously. Better yet, browsers will do some analysis of the resources needed before sending the async request to the network.

Based on observational experimentation, most platforms simply use a glorified for loop when parsing the HTML and often request the resources synchronously. This might be ok for fast wifi experiences, but it can cause inconsistent experiences on flaky wifi.

For example, iMessage will discover and load all <link rel="icon" > favicon, all <meta property="og:image" images, and all <meta name="twitter:image:src" before deciding what to render. Many sites still advertise 5 or more favicon sizes. This means that iMessage will download all favicons regardless of size and then not use them if it decides to instead render the image.

For this reason the meta markup that is included is important. The lighter the content, the more likely it will be to be rendered.

5. Markup Matters

Since Microbrowsers are simple-brained browsers, it is all the more important to produce good markup. Here are a few good strategies:

• It’s almost 2020, you only need one favicon size. Remove all the other <link rel="shortcut icon" and <link rel="icon" references.
• Based on observational experimentation, the most commonly recognized microdata tags for preview are the Open-Graph tags. When the OG and twitter card tags are missing, the default SEO <meta name="description" is used. However, since the description is often nonsensical SEO optimized phrases, users’ eyes will likely glaze over.

• On that note, use good descriptive text
• Provide up to three <meta property="og:image" images. Most platforms will only load the first one, while others (notably iMessage) attempts to create a collage.

Figure 6: Amazon uses User-Agent detection which results in many link previews using the description meta tag.

• Use <meta property="og:video* with progressive (not streaming) video experiences.

<meta property="og:type" content="video.other">
<meta property="og:video:url" 
               content="https://shoesbycolin.com/blue.mp4">
<meta property="og:video:secure_url" 
               content="https://shoesbycolin.com/blue.mp4">
<meta property="og:video:type" content="video/mp4">
<meta property="og:video:width" content="1280">
<meta property="og:video:height" content="720">

• Don’t use UA sniffing to hide the <meta> tags. Sites like Amazon do this to try and show only Facebook/Twitter the microdata annotated website. But this can cause problems for some Microbrowsers that don’t use the same impersonation convention. The result is a simple link without a preview.
• Use the opportunity to tell your product story or summarize your ideas.

Summary

As more of our conversations happen in group chats and slack channels, link previews are an important way for you to engage users before they start the journey on your site. Unfortunately, not all websites present good or compelling previews. (And now that you know what to look for, you won’t be able to unsee bad examples - I’m sorry). To help users take the leap and visit your site, we need to make sure that all our pages are annotated with microdata. Better yet, we can use these previews to create compelling visual summaries.

About the author

Colin is part of the CTO Office at Cloudinary and co-author of the O’Reilly book High Performance Images. He spends much of his time at the intersection of high volume data, media, browsers and standards. He recently helped the community effort writing chapters in the Web Almanac on Media and CDNs. You can find him on tweeting @colinbendell and at blogging at https://bendell.ca

More articles by Colin

Cambridge, Mass. : National Bureau of Economic Research, 2020

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