Tag: Native

Copy the Browser’s Native Focus Styles

Remy documented this the other day. Firefox supports a Highlight keyword and both Chrome and Safari support a -webkit-focus-ring-color keyword. So if you, for example, have removed focus from something and want to put it back in the same style as the browser default, or want to apply a focus style to an element when it isn’t directly in focus itself, this can be useful.

For example:

button:focus + span {   outline: 5px auto Highlight;   outline: 5px auto -webkit-focus-ring-color; }

Looks good to me. It’s especially helpful with the sorta weird new Chrome double-outline style that would be slightly tricky to replicate otherwise.

Chrome 84
Safari 13.1
Firefox 80


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Striking a Balance Between Native and Custom Select Elements

Here’s the plan! We’re going to build a styled select element. Not just the outside, but the inside too. Total styling control. Plus we’re going to make it accessible. We’re not going to try to replicate everything that the browser does by default with a native <select> element. We’re going to literally use a <select> element when any assistive tech is used. But when a mouse is being used, we’ll show the styled version and make it function as a select element.

That’s what I mean by “hybrid” selects: they are both a native <select> and a styled alternate select in one design pattern.

Custom selects (left) are often used in place of native selects (right) for aesthetics and design consistency.

Select, dropdown, navigation, menu… the name matters

While doing the research for this article, I thought about many names that get tossed around when talking about selects, the most common of which are “dropdown” and “menu.” There are two types of naming mistakes we could make: giving the same name to different things, or giving different names to the same thing. A select can suffer from both mistakes.

Before we move ahead, let me try to add clarity around using “dropdown” as a term. Here’s how I define the meaning of dropdown:

Dropdown: An interactive component that consists of a button that shows and hides a list of items, typically on mouse hover, click or tap. The list is not visible by default until the interaction starts. The list usually displays a block of content (i.e. options) on top of other content.

A lot of interfaces can look like a dropdown. But simply calling an element a “dropdown” is like using “fish” to describe an animal. What type of fish it is? A clownfish is not the same as a shark. The same goes for dropdowns.

Like there are different types of fish in the sea, there are different types of components that we might be talking about when we toss the word “dropdown” around:

  • Menu: A list of commands or actions that the user can perform within the page content.
  • Navigation: A list of links used for navigating through a website.
  • Select: A form control (<select>) that displays a list of options for the user to select within a form.

Deciding what type of dropdown we’re talking about can be a foggy task. Here are some examples from around the web that match how I would classify those three different types. This is based on my research and sometimes, when I can’t find a proper answer, intuition based on my experience.

Dropdown-land: Five scenarios where different dropdowns are used across the internet. Read the table below for a detailed description.
Diagram Label Scenario Dropdown Type
1 The dropdown expects a selected option to be submitted within a form context (e.g. Select Age) Select
2 The dropdown does not need an active option (e.g. A list of actions: copy, paste and cut) Menu
3 The selected option influences the content. (e.g. sorting list) Menu or Select (more about it later)
4 The dropdown contains links to other pages. (e.g. A “meganav” with websites links) Disclosure Navigation
5 The dropdown has content that is not a list. (e.g. a date picker) Something else that should not be called dropdown

Not everyone perceives and interacts with the internet in the same way. Naming user interfaces and defining design patterns is a fundamental process, though one with a lot of room for personal interpretation. All of that variation is what drives the population of dropdown-land. 

There is a dropdown type that is clearly a menu. Its usage is a hot topic in conversations about accessibility. I won’t talk much about it here, but let me just reinforce that the <menu> element is deprecated and no longer recommended. And here’s a detailed explanation about inclusive menus and menus buttons, including why ARIA menu role should not be used for site navigation.

We haven’t even touched on other elements that fall into a rather gray area that makes classifying dropdowns even murkier because of a lack of practical uses cases from the WCAG community.

Uff… that was a lot. Let’s forget about this dropdown-land mess and focus exclusively on the dropdown type that is clearly a <select> element.

Let’s talk about <select>

Styling form controls is an interesting journey. As MDN puts it, there’s the good, the bad, and the ugly. Good is stuff like <form> which is just a block-level element to style. Bad is stuff like checkboxes, which can be done but is somewhat cumbersome. <select> is definitely in ugly terrain.

A lot of articles have been written about it and, even in 2020, it’s still a challenge to create custom selects and some users still prefer the simple native ones

Among developers, the <select> is the most frustrating form control by far, mainly because of its lack of styling support. The UX struggle behind it is so big that we look for other alternatives. Well, I guess the first rule of <select> is similar to ARIA: avoid using it if you can.

I could finish the article right here with “Don’t use <select>, period.” But let’s face reality: a select is still our best solution in a number of circumstances. That might include scenarios where we’re working with a list that contains a lot of options, layouts that are tight on space, or simply a lack of time or budget to design and implement a great custom interactive component from scratch.

Custom <select> requirements

When we make the decision to create a custom select — even if it’s just a “simple” one — these are the requirements we generally have to work with:

  • There is a button that contains the current selected option.
  • Clicking the box toggles the visibility of the options list (also called listbox).
  • Clicking an option in the listbox updates the selected value. The button text changes and the listbox is closed.
  • Clicking outside the component closes the listbox.
  • The trigger contains a small triangle icon pointing downward to indicate there are options.

Something like this:

Some of you may be thinking this works and is good to go. But wait… does it work for everyone?  Not everyone uses a mouse (or touch screen). Plus, a native <select> element comes with more features we get for free and aren’t included in those requirements, such as:

  • The checked option is perceivable for all users regardless of their visual abilities.
  • The component can interact with a keyboard in a predictable way across all browsers (e.g. using arrow keys to navigate, Enter to select, Esc to cancel, etc.).
  • Assistive technologies (e.g. screen readers) announce the element clearly to users, including its role, name and state.
  • The listbox position is adjusted. (i.e. does not get cut off of the screen).
  • The element respects the user’s operating system preferences (e.g high contrast, color scheme, motion, etc.).

This is where the majority of the custom selects fail in some way. Take a look at some of the major UI components libraries. I won’t mention any because the web is ephemeral, but go give it a try. You’ll likely notice that the select component in one framework behaves differently from another. 

Here are additional characteristics to watch for:

  • Is a listbox option immediately activated on focus when navigating with a keyboard?
  • Can you use Enter and/or Space to select an option?
  • Does the Tab key jump go to the next option in the listbox, or jump to the next form control?
  • What happens when you reach the last option in the listbox using arrow keys? Does it simply stay at the last item, does it go back to the first option, or worst of all, does focus move to the next form control? 
  • Is it possible to jump directly to the last item in the listbox using the Page Down key?
  • Is it possible to scroll through the listbox items if there are more than what is currently in view?

This is a small sample of the features included in a native <select> element.

Once we decide to create our own custom select, we are forcing people to use it in a certain way that may not be what they expect.

But it gets worse. Even the native <select> behaves differently across browsers and screen readers. Once we decide to create our own custom select, we are forcing people to use it in a certain way that may not be what they expect. That’s a dangerous decision and it’s in those details where the devil lives.

Building a “hybrid” select

When we build a simple custom select, we are making a trade-off without noticing it. Specifically, we sacrifice functionality to aesthetics. It should be the other way around.

What if we instead deliver a native select by default and replace it with a more aesthetically pleasing one if possible? That’s where the “hybrid” select idea comes into action. It’s “hybrid” because it consists of two selects, showing the appropriate one at the right moment:

  • A native select, visible and accessible by default
  • A custom select, hidden until it’s safe to be interacted with a mouse

Let’s start with markup. First, we’ll add a native <select> with <option> items before the custom selector for this to work. (I’ll explain why in just a bit.)

Any form control must have a descriptive label. We could use <label>, but that would focus the native select when the label is clicked. To prevent that behavior, we’ll use a <span> and connect it to the select using aria-labelledby.

Finally, we need to tell Assistive Technologies to ignore the custom select, using aria-hidden="true". That way, only the native select is announced by them, no matter what.

<span class="selectLabel" id="jobLabel">Main job role</span> <div class="selectWrapper">   <select class="selectNative js-selectNative" aria-labelledby="jobLabel">     <!-- options -->     <option></option>   </select>   <div class="selectCustom js-selectCustom" aria-hidden="true">      <!-- The beautiful custom select -->   </div> </div>

This takes us to styling, where we not only make things look pretty, but where we handle the switch from one select to the other. We need just a few new declarations to make all the magic happen.

First, both native and custom selects must have the same width and height. This ensures people don’t see major differences in the layout when a switch happens.

.selectNative, .selectCustom {   position: relative;   width: 22rem;   height: 4rem; }

There are two selects, but only one can dictate the space that holds them. The other needs to be absolutely positioned to take it out of the document flow. Let’s do that to the custom select because it’s the “replacement” that’s used only if it can be. We’ll hide it by default so it can’t be reached by anyone just yet.

.selectCustom {   position: absolute;   top: 0;   left: 0;   display: none; }

Here comes the “funny” part. We need to detect if someone is using a device where hover is part of the primary input, like a computer with a mouse. While we typically think of media queries for responsive breakpoints or checking feature support, we can use it to detect hover support too using @media query (hover :hover), which is supported by all major browsers. So, let’s use it to show the custom select only on devices that have hover:

@media (hover: hover) {   .selectCustom {     display: block;   } }

Great, but what about people who use a keyboard to navigate even in devices that have hover? What we’ll do is hide the custom select when the native select is in focus. We can reach for an adjacent Sibling combinatioron (+). When the native select is in focus, hide the custom select next to it in the DOM order. (This is why the native select should be placed before the custom one.)

@media (hover: hover) {   .selectNative:focus + .selectCustom {     display: none;   } }

That’s it! The trick to switch between both selects is done! There are other CSS ways to do it, of course, but this works nicely.

Last, we need a sprinkle of JavaScript. Let’s add some event listeners:

  • One for click events that trigger the custom select to open and reveal the options
  • One to sync both selects values. When one select value is changed, the other select value updates as well
  • One for basic keyboard navigation controls, like navigation with Up and Down keys, selecting options with the Enter or Space keys, and closing the select with Esc

Usability testing

I conducted a very small usability test where I asked a few people with disabilities to try the hybrid select component. The following devices and tools were tested using the latest versions of Chrome (81), Firefox (76) and Safari (13):

  • Desktop device using mouse only
  • Desktop device using keyboard only
  • VoiceOver on MacOS using keyboard
  • NVDA on Windows using keyboard
  • VoiceOver on iPhone and iPad using Safari

All these tests worked as expected, but I believe this could have even more usability tests with more diverse people and tools. If you have access to other devices or tools — such as JAWS, Dragon, etc. — please tell me how the test goes.

An issue was found during testing. Specifically, the issue was with the VoiceOver setting “Mouse pointers: Moves Voice Over cursor.” If the user opens the select with a mouse, the custom select will be opened (instead of the native) and the user won’t experience the native select.

What I most like about this approach is how it uses the best of both worlds without compromising the core functionality:

  • Users on mobile and tablets get the native select, which generally offers a better user experience than a custom select, including performance benefits.
  • Keyboard users get to interact with the native select the way they would expect.
  • Assistive Technologies can interact with the native select like normal.
  • Mouse users get to interact with the enhanced custom select.

This approach provides essential native functionality for everyone without the extra huge code effort to implement all the native features.

Don’t get me wrong. This technique is not a one-size-fits-all solution. It may work for simple selects but probably won’t work for cases that involve complex interactions. In those cases, we’d need to use ARIA and JavaScript to complement the gaps and create a truly accessible custom select.

A note about selects that look like menus

Let’s take a look back at the third Dropdown-land scenario. If you recall, it’s  a dropdown that always has a checked option (e.g. sorting some content). I classified it in the gray area, as either a menu or a select. 

Here’s my line of thought: Years ago, this type of dropdown was implemented mostly using a native <select>. Nowadays, it is common to see it implemented from scratch with custom styles (accessible or not). What we end up with is a select element that looks like a menu. 

Three similar dropdowns that always have a selected option.

A <select>  is a type of menu. Both have similar semantics and behavior, especially in a scenario that involves a list of options where one is always checked.  Now, let me mention the WCAG 3.2.2 On Input (Level A) criterion:

Changing the setting of any user interface component should not automatically cause a change of context unless the user has been advised of the behavior before using the component.

Let’s put this in practice. Imagine a sortable list of students. Visually, it may be obvious that sorting is immediate, but that’s not necessarily true for everyone. So, when using <select>, we risk failing the WCAG guideline because the page content changed, and ignificantly re-arranging the content of a page is considered a change of context.

To ensure the criterion success, we must warn the user about the action before they interact with the element, or include a <button> immediately after the select to confirm the change.

<label for="sortStudents">   Sort students   <!-- Warn the user about the change when a confirmation button is not present. -->   <span class="visually-hidden">(Immediate effect upon selection)</span> </label> <select id="sortStudents"> ... </select>

That said, using a <select> or building a custom menu are both good approaches when it comes to simple menus that change the page content. Just remember that your decision will dictate the amount of work required to make the component fully accessible. This is a scenario where the hybrid select approach could be used.

Final words

This whole idea started as an innocent CSS trick but, after all of this research, I was reminded once more that creating unique experiences without compromising accessibility is not an easy task.

Building truly accessible select components (or any kind of dropdown) is harder than it looks. WCAG provides excellent guidance and best practices, but without specific examples and diverse practical uses cases, the guidelines are mostly aspirational. That’s not to mention the fact that ARIA support is tepid and that native <select> elements look and behave differently across browsers.

The “hybrid” select is just another attempt to create a good looking select while getting as many native features as possible. Don’t look at this technique experiment as an excuse to downplay accessibility, but rather as an attempt to serve both worlds. If you have the resources, time and the needed skills, please do it right and make sure to test it with different users before shipping your component to the world.

P.S. Remember to use a proper name when making a “dropdown” component. 😉

The post Striking a Balance Between Native and Custom Select Elements appeared first on CSS-Tricks.

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Native Image Lazy Loading in Chrome Is Way Too Eager

Interesting research from Aaron Peters on <img loading="lazy" ... >:

On my 13 inch macbook, with Dock positioned on the left, the viewport height in Chrome is 786 pixels so images with loading="lazy" that are more than 4x the viewport down the page are eagerly fetched by Chrome on page load.

In my opinion, that is waaaaay too eager. Why not use a lower threshold value like 1000 pixels? Or even better: base the threshold value on the actual viewport height.

My guess is they chose not to over-engineer the feature by default and will improve it over time. By choosing a fairly high threshold, they ran a lower risk of it annoying users with layout shifts on pages with images that don’t use width/height attributes.

I think this unmerged Pull Request is the closest thing we have to a spec and it uses language like “scrolled into the viewport” which suggests no threshold at all.

Direct Link to ArticlePermalink

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Weekly Platform News: Contrast Ratio Range, replaceAll Method, Native File System API

In this week’s roundup: Firefox’s new contrast checker, a simpler way to lasso substrings in a string, and a new experimental API that will let apps fiddle with a user’s local files.

Firefox shows the contrast ratio range for text on a multicolored background

According to Success Criterion 1.4.3 of the Web Content Accessibility Guidelines (WCAG), text should have a contrast ratio of at least 4.5. (A lower contrast ratio is acceptable only if the text is 24px or larger.)

If the background of the text is not a solid color but a color gradient or photograph, you can use the special element picker in Firefox’s Accessibility panel to get a range of contrast ratios based on the element’s actual background.

(via Šime Vidas)

Replacing all instances of a substring in a string

The new JavaScript replaceAll method makes it easier to replace all instances of a substring in a string without having to convert the substring to a regex first, which is “hard to get right since JavaScript doesn’t offer a built-in mechanism to escape regular expression patterns.”

// BEFORE str = str.replace(/foo/g, "bar");  // AFTER str = str.replaceAll("foo", "bar");

This new string method has not yet shipped in browsers, but you can start using it today via Babel (since it’s automatically polyfilled by @babel/preset-env).

(via Mathias Bynens)

Try out the Native File System API in Chrome

The Native File System API, which is experimentally supported in Chrome, allows web apps to read or save changes directly to local files on the person’s computer. The app is granted permission to view and edit files in a specific folder via two separate prompts.

You can try out this new feature by visiting labs.vaadin.com in Chrome on desktop.

(via Thomas Steiner)

More news…

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The post Weekly Platform News: Contrast Ratio Range, replaceAll Method, Native File System API appeared first on CSS-Tricks.

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Comparing the Different Types of Native JavaScript Popups

JavaScript has a variety of built-in popup APIs that display special UI for user interaction. Famously:

alert("Hello, World!");

The UI for this varies from browser to browser, but generally you’ll see a little window pop up front and center in a very show-stopping way that contains the message you just passed. Here’s Firefox and Chrome:

Native popups in Firefox (left) and Chrome (right). Note the additional UI preventing additional dialogs in Firefox from triggering it more than once. You can also see how Chrome is pinned to the top of the window.

There is one big problem you should know about up front

JavaScript popups are blocking.

The entire page essentially stops when a popup is open. You can’t interact with anything on the page while one is open — that’s kind of the point of a “modal” but it’s still a UX consideration you should be keenly aware of. And crucially, no other main-thread JavaScript is running while the popup is open, which could (and probably is) unnecessarily preventing your site from doing things it needs to do.

Nine times out of ten, you’d be better off architecting things so that you don’t have to use such heavy-handed stop-everything behavior. Native JavaScript alerts are also implemented by browsers in such a way that you have zero design control. You can’t control *where* they appear on the page or what they look like when they get there. Unless you absolutely need the complete blocking nature of them, it’s almost always better to use a custom user interface that you can design to tailor the experience for the user.

With that out of the way, let’s look at each one of the native popups.

window.alert();

window.alert("Hello World");  <button onclick="alert('Hello, World!');">Show Message</button>  const button = document.querySelectorAll("button"); button.addEventListener("click", () => {   alert("Text of button: " + button.innerText); });

See the Pen
alert("Example");
by Elliot KG (@ElliotKG)
on CodePen.

What it’s for: Displaying a simple message or debugging the value of a variable.

How it works: This function takes a string and presents it to the user in a popup with a button with an “OK” label. You can only change the message and not any other aspect, like what the button says.

The Alternative: Like the other alerts, if you have to present a message to the user, it’s probably better to do it in a way that’s tailor-made for what you’re trying to do.

If you’re trying to debug the value of a variable, consider console.log(<code>"`Value of variable:"`, variable); and looking in the console.

window.confirm();

window.confirm("Are you sure?");  <button onclick="confirm('Would you like to play a game?');">Ask Question</button>  let answer = window.confirm("Do you like cats?"); if (answer) {   // User clicked OK } else {   // User clicked Cancel }

See the Pen
confirm("Example");
by Elliot KG (@ElliotKG)
on CodePen.

What it’s for: “Are you sure?”-style messages to see if the user really wants to complete the action they’ve initiated.

How it works: You can provide a custom message and popup will give you the option of “OK” or “Cancel,” a value you can then use to see what was returned.

The Alternative: This is a very intrusive way to prompt the user. As Aza Raskin puts it:

…maybe you don’t want to use a warning at all.”

There are any number of ways to ask a user to confirm something. Probably a clear UI with a <button>Confirm</button> wired up to do what you need it to do.

window.prompt();

window.prompt("What’s your name?");   let answer = window.prompt("What is your favorite color?"); // answer is what the user typed in, if anything

See the Pen
prompt("Example?", "Default Example");
by Elliot KG (@ElliotKG)
on CodePen.

What it’s for: Prompting the user for an input. You provide a string (probably formatted like a question) and the user sees a popup with that string, an input they can type into, and “OK” and “Cancel” buttons.

How it works: If the user clicks OK, you’ll get what they entered into the input. If they enter nothing and click OK, you’ll get an empty string. If they choose Cancel, the return value will be null.

The Alternative: Like all of the other native JavaScript alerts, this doesn’t allow you to style or position the alert box. It’s probably better to use a <form> to get information from the user. That way you can provide more context and purposeful design.

window.onbeforeunload();

window.addEventListener("beforeunload", () => {   // Standard requires the default to be cancelled.   event.preventDefault();   // Chrome requires returnValue to be set (via MDN)   event.returnValue = ''; });

See the Pen
Example of beforeunload event
by Chris Coyier (@chriscoyier)
on CodePen.

What it’s for: Warn the user before they leave the page. That sounds like it could be very obnoxious, but it isn’t often used obnoxiously. It’s used on sites where you can be doing work and need to explicitly save it. If the user hasn’t saved their work and is about to navigate away, you can use this to warn them. If they *have* saved their work, you should remove it.

How it works: If you’ve attached the beforeunload event to the window (and done the extra things as shown in the snippet above), users will see a popup asking them to confirm if they would like to “Leave” or “Cancel” when attempting to leave the page. Leaving the site may be because the user clicked a link, but it could also be the result of clicking the browser’s refresh or back buttons. You cannot customize the message.

MDN warns that some browsers require the page to be interacted with for it to work at all:

To combat unwanted pop-ups, some browsers don’t display prompts created in beforeunload event handlers unless the page has been interacted with. Moreover, some don’t display them at all.

The Alternative: Nothing that comes to mind. If this is a matter of a user losing work or not, you kinda have to use this. And if they choose to stay, you should be clear about what they should to to make sure it’s safe to leave.

Accessibility

Native JavaScript alerts used to be frowned upon in the accessibility world, but it seems that screen readers have since become smarter in how they deal with them. According to Penn State Accessibility:

The use of an alert box was once discouraged, but they are actually accessible in modern screen readers.

It’s important to take accessibility into account when making your own modals, but there are some great resources like this post by Ire Aderinokun to point you in the right direction.

General alternatives

There are a number of alternatives to native JavaScript popups such as writing your own, using modal window libraries, and using alert libraries. Keep in mind that nothing we’ve covered can fully block JavaScript execution and user interaction, but some can come close by greying out the background and forcing the user to interact with the modal before moving forward.

You may want to look at HTML’s native <dialog> element. Chris recently took a hands-on look) at it. It’s compelling, but apparently suffers from some significant accessibility issues. I’m not entirely sure if building your own would end up better or worse, since handling modals is an extremely non-trivial interactive element to dabble in. Some UI libraries, like Bootstrap, offer modals but the accessibility is still largely in your hands. You might to peek at projects like a11y-dialog.

Wrapping up

Using built-in APIs of the web platform can seem like you’re doing the right thing — instead of shipping buckets of JavaScript to replicate things, you’re using what we already have built-in. But there are serious limitations, UX concerns, and performance considerations at play here, none of which land particularly in favor of using the native JavaScript popups. It’s important to know what they are and how they can be used, but you probably won’t need them a heck of a lot in production web sites.

The post Comparing the Different Types of Native JavaScript Popups appeared first on CSS-Tricks.

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A Deep Dive into Native Lazy-Loading for Images and Frames

Today’s websites are packed with heavy media assets like images and videos. Images make up around 50% of an average website’s traffic. Many of them, however, are never shown to a user because they’re placed way below the fold.

What’s this thing about images being lazy, you ask? Lazy-loading is something that’s been covered quite a bit here on CSS-Tricks, including a thorough guide with documentation for different approaches using JavaScript. In short, we’re talking about a mechanism that defers the network traffic necessary to load content when it’s needed — or rather when trigger the load when the content enters the viewport.

The benefit? A smaller initial page that loads faster and saves network requests for items that may not be needed if the user never gets there.

If you read through other lazy-loading guides on this or other sites, you’ll see that we’ve had to resort to different tactics to make lazy-loading work. Well, that’s about to change when lazy-loading will be available natively in HTML as a new loading attribute… at least in Chrome which will hopefully lead to wider adoption. Chrome has already merged the code for native lazy-loading and is expected to ship it in Chrome 75, which is slated to release June 4, 2019.

Eager cat loaded lazily (but still immediately because it's above the fold)

The pre-native approach

Until now, developers like ourselves have had to use JavaScript (whether it’s a library or something written from scratch) in order to achieve lazy-loading. Most libraries work like this:

  • The initial, server-side HTML response includes an img element without the src attribute so the browser does not load any data. Instead, the image’s URL is set as another attribute in the element’s data set, e. g. data-src.
  • <img data-src="https://tiny.pictures/example1.jpg" alt="...">
  • Then, a lazy-loading library is loaded and executed.
  • <script src="LazyLoadingLibrary.js"></script> <script>LazyLoadingLibrary.run()</script>
  • That keeps track of the user’s scrolling behavior and tells the browser to load the image when it is about to be scrolled into view. It does that by copying the data-src attribute’s value to the previously empty src attribute.
  • <img src="https://tiny.pictures/example1.jpg" data-src="https://tiny.pictures/example1.jpg" alt="...">

This has worked for a pretty long time now and gets the job done. But it’s not ideal for good reasons.

The obvious problem with this approach is the length of the critical path for displaying the website. It consists of three steps, which have to be carried out in sequence (after each other):

  1. Load the initial HTML response
  2. Load the lazy-loading library
  3. Load the image file

If this technique is used for images above the fold the website will flicker during loading because it is first painted without the image (after step 1 or 2, depending on if the script uses defer or async) and then — after having been loaded — include the image. It will also be perceived as loading slowly.

In addition, the lazy-loading library itself puts an extra weight on the website’s bandwidth and CPU requirements. And let’s not forget that a JavaScript approach won’t work for people who have JavaScript disabled (although we shouldn’t really care about them in 2019, should we?).

Oh, and what about sites that rely on RSS to distribute content, like CSS-Tricks? The initial image-less render means there are no images in the RSS version of content as well.

And so on.

Native lazy-loading to the rescue!

Lazy cat loaded lazily

As we noted at the start, Chromium and Google Chrome will ship a native lazy-loading mechanism in the form of a new loading attribute, starting in Chrome 75. We’ll go over the attribute and its values in just a bit, but let’s first get it working in our browsers so we can check it out together.

Enable native lazy-loading

Until Chrome 75 is officially released, we have Chrome Canary and can enable lazy-loading manually by switching two flags.

  1. Open chrome://flags in Chromium or Chrome Canary.
  2. Search for lazy.
  3. Enable both the “Enable lazy image loading” and the “Enable lazy frame loading” flag.
  4. Restart the browser with the button in the lower right corner of the screen.
Native lazy-loading flags in Google Chrome

You can check if the feature is properly enabled by opening your JavaScript console (F12). You should see the following warning:

[Intervention] Images loaded lazily and replaced with placeholders. Load events are deferred.”

All set? Now we get to dig into the loading attribute.

The loading attribute

Both the img and the iframe elements will accept the loading attribute. It’s important to note that its values will not be taken as a strict order by the browser but rather as a hint to help the browser make its own decision whether or not to load the image or frame lazily.

The attribute can have three values which are explained below. Next to the images, you’ll find tables listing your individual resource loading timings for this page load. Range response refers to a kind of partial pre-flight request made to determine the image’s dimensions (see How it works) for details). If this column is filled, the browser made a successful range request.

Please note the startTime column, which states the time image loading was deferred after the DOM had been parsed. You might have to perform a hard reload (CTRL + Shift + R) to re-trigger range requests.

The auto (or unset) value

<img src="auto-cat.jpg" loading="auto" alt="..."> <img src="auto-cat.jpg" alt="..."> <iframe src="https://css-tricks.com/" loading="auto"></iframe> <iframe src="https://css-tricks.com/"></iframe>
Auto cat loaded automatically
Auto cat loaded automatically

Setting the loading attribute to auto (or simply leaving the value blank, as in loading="") lets the browser decide whether or not to lazy-load an image. It takes many things into consideration to make that decision, like the platform, whether Data Saver mode is enabled, network conditions, image size, image vs. iframe, the CSS display property, among others. (See How it works) for info about why all this is important.)

The eager value

<img src="auto-cat.jpg" loading="eager" alt="..."> <iframe src="https://css-tricks.com/" loading="eager"></iframe>
Eager cat loaded eagerly
Eager cat loaded eagerly

The eager value provides a hint to the browser that an image should be loaded immediately. If loading was already deferred (e. g. because it had been set to lazy and was then changed to eager by JavaScript), the browser should start loading the image immediately.

The lazy value

<img src="auto-cat.jpg" loading="lazy" alt="..."> <iframe src="https://css-tricks.com/" loading="lazy"></iframe>
Lazy cat loaded lazily
Lazy cat loaded lazily

The lazy value provides a hints to the browser that an image should be lazy-loaded. It’s up to the browser to interpret what exactly this means, but the explainer document states that it should start loading when the user scrolls “near” the image such that it is probably loaded once it actually comes into view.

How the loading attribute works

In contrast to JavaScript lazy-loading libraries, native lazy-loading uses a kind of pre-flight request to get the first 2048 bytes of the image file. Using these, the browser tries to determine the image’s dimensions in order to insert an invisible placeholder for the full image and prevent content from jumping during loading.

The image’s load event is fired as soon as the full image is loaded, be it after the first request (for images smaller than 2 KB) or after the second one. Please note that the load event may never be fired for certain images because the second request is never made.

In the future, browsers might make twice as many image requests as there would be under the current proposal. First the range request, then the full request. Make sure your servers support the HTTP Range: 0-2047 header and respond with status code 206 (Partial Content) to prevent them from delivering the full image twice.

Due to the higher number of subsequent requests made by the same user, web server support for the HTTP/2 protocol will become more important.

Let’s talk about deferred content. Chrome’s rendering engine Blink uses heuristics to determine which content should be deferred and for how long to defer it. You can find a comprehensive list of requirements in Scott Little’s design documentation. This is a short breakdown of what will be deferred:

  • Images and frames on all platforms which have loading="lazy" set
  • Images on Chrome for Android with Data Saver enabled and that satisfy all of the following:
    • loading="auto" or unset
    • no width and height attributes smaller than 10px
    • not created programmatically in JavaScript
  • Frames which satisfy all of the following:
    • loading="auto" or unset
    • is from a third-party (different domain or protocol than the embedding page)
    • larger than 4 pixels in height and width (to prevent deferring tiny tracking frames)
    • not marked as display: none or visibility: hidden (again, to prevent deferring tracking frames)
    • not positioned off-screen using negative x or y coordinates

Responsive images with srcset

Native lazy-loading also works with responsive img elements using the srcset attribute. This attribute offers a list of image file candidates to the browser. Based on the user’s screen size, display pixel ratio, network conditions, etc., the browser will choose the optimal image candidate for the occasion. Image optimization CDNs like tiny.pictures are able to provide all image candidates in real-time without any back end development necessary.

<img src="https://demo.tiny.pictures/native-lazy-loading/lazy-cat.jpg" srcset="https://demo.tiny.pictures/native-lazy-loading/lazy-cat.jpg?width=400 400w, https://demo.tiny.pictures/native-lazy-loading/lazy-cat.jpg?width=800 800w" loading="lazy" alt="...">

Browser support

At the time of this writing, no browser supports native-loading by default. However, Chrome will enable the feature, as we’ve covered, starting in Chrome 75. No other browser vendor has announced support so far. (Edge being a kind of exception because it will soon make the switch to Chromium.)

You can detect the feature with a few lines of JavaScript:

if ("loading" in HTMLImageElement.prototype) {   // Support. } else {   // No support. You might want to dynamically import a lazy-loading library here (see below). }

See the Pen
Native lazy-loading browser support
by Erk Struwe (@erkstruwe)
on CodePen.

Automatic fallback to JavaScript solution with low-quality image placeholder

One very cool feature of most JavaScript-based lazy-loading libraries is the low-quality image placeholder (LQIP). Basically, it leverages the idea that browsers load (or perhaps I should say used to load) the src of an img element immediately, even if it gets later replaced by another URL. This way, it’s possible to load a tiny file size, low-quality image file on page load and later replace it with a full-sized version.

We can now use this to mimic the native lazy-loading’s 2 KB range requests in browsers that do not support this feature in order to achieve the same result, namely a placeholder with the actual image dimensions and a tiny file size.

See the Pen
Native lazy-loading with JavaScript library fallback and low-quality image placeholder
by Erk Struwe (@erkstruwe)
on CodePen.

Conclusion

I’m really excited about this feature. And frankly, I’m still wondering why it hasn’t got much more attention until now, given the fact that its release is imminent and the impact on global internet traffic will be remarkable, even if only small parts of the heuristics are changed.

Think about it: After a gradual roll-out for the different Chrome platforms and with auto being the default setting, the world’s most popular browser will soon lazy-load below-the-fold images and frames by default. Not only will the traffic amount of many badly-written websites drop significantly, but web servers will be hammered with tiny requests for image dimension detection.

And then there’s tracking: Assuming many unsuspecting tracking pixels and frames will be prevented from being loaded, the analytics and affiliate industry will have to act. We can only hope they don’t panic and add loading="eager" to every single image, rendering this great feature useless for their users. They should rather change their code to be recognized as tracking pixels by the heuristics described above.

Web developers, analytics and operations managers should check their website’s behavior with this feature and their servers’ support for Range requests and HTTP/2 immediately.

Image optimization CDNs could help out in case there are any issues to be expected or if you’d like to take image delivery optimization to the max (including automatic WebP support, low-quality image placeholders, and much more). Read more about tiny.pictures!

References

The post A Deep Dive into Native Lazy-Loading for Images and Frames appeared first on CSS-Tricks.

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Native Lazy Loading

IntersectionObserver has made lazy loading a lot easier and more efficient than it used to be, but to do it really right you still gotta remove the src and such, which is cumbersome. It’s definitely not as easy as:

<img src="celebration.jpg" loading="lazy" alt="..." />

Addy Osmani says it’s coming in Chrome 75:

The loading attribute allows a browser to defer loading offscreen images and iframes until users scroll near them. loading supports three values:

  • lazy: is a good candidate for lazy loading.
  • eager: is not a good candidate for lazy loading. Load right away.
  • auto: browser will determine whether or not to lazily load.

I’ll probably end up writing a WordPress content filter for this site that adds that attribute for every dang image on this site. Hallelujah, I say, and godspeed other browsers.

Easy lazy loading of images will have the biggest impact on the site as a whole, but lazy loaded iframes will be even bigger for the individual sites that use them. I’m into it.

I hope this pushes along the need for native aspect ratios as well, since a major reason for that is preventing content reflow from things loading later. We do have ways now, though.

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Better Than Native

Andy Bell wrote up his thoughts about the whole web versus native app debate which I think is super interesting. It was hard to make it through the post because I was nodding so aggressively as I read:

The whole idea of competing with native apps seems pretty daft to me, too. The web gives us so much for free that app developers could only dream of, like URLs and the ability to publish to the entire world for free, immediately.

[…] I believe in the web and will continue to believe that building Progressive Web Apps that embrace the web platform will be far superior to the non-inclusive walled garden that is native apps and their app stores. I just wish that others thought like that, too.

Andy also quotes Jeremy Keith making a similar claim to bolster the point:

If the goal of the web is just to compete with native, then we’ve set the bar way too low.

I entirely agree with both Andy and Jeremy. The web should not compete with native apps that are locked within a store. The web should be betterin every way — it can be faster and more beautiful, have better interactions, and smoother animations. We just need to get to work.

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Native Video on the Web

TIL about the HLS video format:

HLS stands for HTTP Live Streaming. It’s an adaptive bitrate streaming protocol developed by Apple. One of those sentences to casually drop at any party. Äh. Back on track: HLS allows you to specify a playlist with multiple video sources in different resolutions. Based on available bandwidth these video sources can be switched and allow adaptive playback.

This is an interesting journey where the engineering team behind Kitchen Stories wanted to switch away from the Vimeo player (160 kB), but still use Vimeo as a video host because they provide direct video links with a Pro plan. Instead, they are using the native <video> element, a library for handling HLS, and a wrapper element to give them a little bonus UX.

This video stuff is hard to keep up with! There is another new format called AV1 that is apparently a big deal as YouTube and Netflix are both embracing it. Andrey Sitnik wrote about it here:

Even though AV1 codec is still considered experimental, you can already leverage its high-quality, low-bitrate features for a sizable chunk for your web audience (users with current versions of Chrome and Firefox). Of course, you would not want to leave users for other browsers hanging, but the attributes for <video> and <source> tags make implementing this logic easy, and in pure HTML, you don’t need to go at length to detect user agents with JavaScript.

That doesn’t even mention HLS, but I suppose that’s because HSL is a streaming protocol, which still needs to stream in some sort of format.

Direct Link to ArticlePermalink

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JavaScript to Native (and Back!)

I admit I’m quite intrigued by frameworks that allow you write apps in web frameworks because they do magic to make them into native apps for you. There are loads of players here. You’ve got NativeScript, Cordova, PhoneGap, Tabris, React Native, and Flutter. For deskop apps, we’ve got Electron.

What’s interesting now is to see what’s important to these frameworks by honing in on their focus. Hummingbird is Flutter for the web. (There is a fun series on Flutter over on the Bendworks blog in addition to a post we published earlier this year.) The idea being you get super high performance ,thanks to the framework, and you’ve theoretically built one app that runs both on the web and natively. I don’t know of any real success stories I can point to, but it does seem like an awesome possibility.

Nicolas Gallagher has been a strong proponent of React Native for the web.

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