Journal tags: buttons

3

sparkline

A polyfill for button type=”share”

After writing about a declarative Web Share API here yesterday I thought I’d better share the idea (see what I did there?).

I opened an issue on the Github repo for the spec.

(I hope that’s the right place for this proposal. I know that in the past ideas were kicked around on the Discourse site for Web platform Incubator Community Group but I can’t stand Discourse. It literally requires JavaScript to render anything to the screen even though the entire content is text. If it turns out that that is the place I should’ve posted, I guess I’ll hold my nose and do it using the most over-engineered reinvention of the browser I’ve ever seen. But I believe that the plan is for WICG to migrate proposals to Github anyway.)

I also realised that, as the JavaScript Web Share API already exists, I can use it to polyfill my suggestion for:

<button type="share">

The polyfill also demonstrates how feature detection could work. Here’s the code.

This polyfill takes an Inception approach to feature detection. There are three nested levels:

  1. This browser supports button type="share". Great! Don’t do anything. Otherwise proceed to level two.
  2. This browser supports the JavaScript Web Share API. Use that API to share the current page URL and title. Otherwise proceed to level three.
  3. Use a mailto: link to prefill an email with the page title as the subject and the URL in the body. Ya basic!

The idea is that, as long as you include the 20 lines of polyfill code, you could start using button type="share" in your pages today.

I’ve made a test page on Codepen. I’m just using plain text in the button but you could use a nice image or SVG or combination. You can use the Codepen test page to observe two of the three possible behaviours browsers could exhibit:

  1. A browser supports button type="share". Currently that’s none because I literally made this shit up yesterday.
  2. A browser supports the JavaScript Web Share API. This is Safari on Mac, Edge on Windows, Safari on iOS, and Chrome, Samsung Internet, and Firefox on Android.
  3. A browser supports neither button type="share" nor the existing JavaScript Web Share API. This is Firefox and Chrome on desktop (and Edge if you’re on a Mac).

See the Pen Polyfill for button type=”share" by Jeremy Keith (@adactio) on CodePen.

The polyfill doesn’t support Internet Explorer 11 or lower because it uses the DOM closest() method. Feel free to fork and rewrite if you need to support old IE.

A declarative Web Share API

I’ve written about the Web Share API before. It’s a handy little bit of JavaScript that—if supported—brings up a system-level way of sharing a page. Seeing as it probably won’t be long before we won’t be able to see full URLs in browsers anymore, it’s going to fall on us as site owners to provide this kind of fundamental access.

Right now the Web Share API exists entirely in JavaScript. There are quite a few browser APIs like that, and it always feels like a bit of a shame to me. Ideally there should be a JavaScript API and a declarative option, even if the declarative option isn’t as powerful.

Take form validation. To cover the most common use cases, you probably only need to use declarative markup like input type="email" or the required attribute. But if your use case gets a bit more complicated, you can reach for the Constraint Validation API in JavaScript.

I like that pattern. I wish it were an option for JavaScript-only APIs. Take the Geolocation API, for example. Right now it’s only available through JavaScript. But what if there were an input type="geolocation" ? It wouldn’t cover all use cases, but it wouldn’t have to. For the simple case of getting someone’s location (like getting someone’s email or telephone number), it would do. For anything more complex than that, that’s what the JavaScript API is for.

I was reminded of this recently when Ada Rose Cannon tweeted:

It really feels like there should be a semantic version of the share API, like a mailto: link

I think she’s absolutely right. The Web Share API has one primary use case: let the user share the current page. If that use case could be met in a declarative way, then it would have a lower barrier to entry. And for anyone who needs to do something more complicated, that’s what the JavaScript API is for.

But Pete LePage asked:

How would you feature detect for it?

Good question. With the JavaScript API you can do feature detection—if the API isn’t supported you can either bail or provide your own implementation.

There a few different ways of extending HTML that allow you to provide a fallback for non-supporting browsers.

You could mint a new element with a content model that says “Browsers, if you do support this element, ignore everything inside the opening and closing tags.” That’s the way that the canvas element works. It’s the same for audio and video—they ignore everything inside them that isn’t a source element. So developers can provide a fallback within the opening and closing tags.

But forging a new element would be overkill for something like the Web Share API (or Geolocation). There are more subtle ways of extending HTML that I’ve already alluded to.

Making a new element is a lot of work. Making a new attribute could also be a lot of work. But making a new attribute value might hit the sweet spot. That’s why I suggested something like input type="geolocation" for the declarative version of the Geolocation API. There’s prior art here; this is how we got input types for email, url, tel, color, date, etc. The key piece of behaviour is that non-supporting browsers will treat any value they don’t understand as “text”.

I don’t think there should be input type="share". The action of sharing isn’t an input. But I do think we could find an existing HTML element with an attribute that currently accepts a list of possible values. Adding one more value to that list feels like an inexpensive move.

Here’s what I suggested:

<button type=”share” value=”title,text”>

For non-supporting browsers, it’s a regular button and needs polyfilling, no different to the situation with the JavaScript API. But if supported, no JS needed?

The type attribute of the button element currently accepts three possible values: “submit”, “reset”, or “button”. If you give it any other value, it will behave as though you gave it a type of “submit” or “button” (depending on whether it’s in a form or not) …just like an unknown type value on an input element will behave like “text”.

If a browser supports button type="share”, then when the user clicks on it, the browser can go “Right, I’m handing over to the operating system now.”

There’s still the question of how to pass data to the operating system on what gets shared. Currently the JavaScript API allows you to share any combination of URL, text, and description.

Initially I was thinking that the value attribute could be used to store this data in some kind of key/value pairing, but the more I think about it, the more I think that this aspect should remain the exclusive domain of the JavaScript API. The declarative version could grab the current URL and the value of the page’s title element and pass those along to the operating system. If you need anything more complex than that, use the JavaScript API.

So what I’m proposing is:

<button type="share">

That’s it.

But how would you test for browser support? The same way as you can currently test for supported input types. Make use of the fact that an element’s attribute value and an element’s property value (which 99% of the time are the same), will be different if the attribute value isn’t supported:

var testButton = document.createElement("button");
testButton.setAttribute("type","share");
if (testButton.type != "share") {
// polyfill
}

So that’s my modest proposal. Extend the list of possible values for the type attribute on the button element to include “share” (or something like that). In supporting browsers, it triggers a very bare-bones handover to the OS (the current URL and the current page title). In non-supporting browsers, it behaves like a button currently behaves.

Programming CSS to perform Sass colour functions

I wrote recently about moving away from Sass to using native CSS features. I had this to say on the topic of mixins in Sass:

These can be very useful, but now there’s a lot that you can do just in CSS with calc(). The built-in darken() and lighten() mixins are handy though when it comes to colours.

I know we will be getting these in the future but we’re not there yet with CSS.

Anyway, I had all this in the back of my mind when I was reading Lea’s excellent feature in this month’s Increment: A user’s guide to CSS variables. She’s written about a really clever technique of combining custom properites with hsl() colour values for creating colour palettes. (See also: Una’s post on dynamic colour theming with pure CSS.)

As so often happens when I’m reading something written by Lea—or seeing her give a talk—light bulbs started popping over my head (my usual response to Lea’s knowledge bombs is either “I didn’t know you could do that!” or “I never thought of doing that!”).

I immediately set about implementing this technique over on The Session. The trick here is to use separate custom properties for the hue, saturation, and lightness parts of hsl() colour values. Then, when you want to lighten or darken the colour—say, on hover—you can update the lightness part.

I’ve made a Codepen to show what I’m doing.

Let’s say I’m styling a button element. I make custom propertes for hsl() values:

button {
  --button-colour-hue: 19;
  --button-colour-saturation: 82%;
  --button-colour-lightness: 38%;
  background-color: hsl(
    var(--button-colour-hue),
    var(--button-colour-saturation),
    var(--button-colour-lightness)
  );
}

For my buttons, I want the borders to be slightly darker than the background colour. When I was using Sass, I used the darken() function to this. Now I use calc(). Here’s how I make the borders 10% darker:

border-color: hsl(
  var(--button-colour-hue),
  var(--button-colour-saturation),
  calc(var(--button-colour-lightness) - 10%)
);

That calc() function is substracting a percentage from a percentage: 38% minus 10% in this case. The borders will have a lightness of 28%.

I make the bottom border even darker and the top border lighter to give a feeling of depth.

On The Session there’s a “cancel” button style that’s deep red.

Here’s how I set its colour:

.cancel {
  --button-colour-hue: 0;
  --button-colour-saturation: 100%;
  --button-colour-lightness: 40%;
}

That’s it. The existing button declarations take care of assigning the right shades for the border colours.

Here’s another example. Site admins see buttons for some actions only available to them. I want those buttons to have their own colour:

.admin {
  --button-colour-hue: 45;
  --button-colour-saturation: 100%;
  --button-colour-lightness: 40%;
}

You get the idea. It doesn’t matter how many differently-coloured buttons I create, the effect of darkening or lightening their borders is all taken care of.

So it turns out that the lighten() and darken() functions from Sass are available to us in CSS by using a combination of custom properties, hsl(), and calc().

I’m also using this combination to lighten or darken background and border colours on :hover. You can poke around the Codepen if you want to see that in action.

I love seeing the combinatorial power of these different bits of CSS coming together. It really is a remarkably powerful programming language.