Tags: dom_scripting

I’m a big fan of HTML5’s datalist element and its elegant design. It’s a way to progressively enhance any input element into a combobox.

You use the list attribute on the input element to point to the ID of the associated datalist element.

<label for="homeworld">Your home planet</label>
<input type="text" name="homeworld" id="homeworld" list="planets">
<datalist id="planets">
 <option value="Mercury">
 <option value="Venus">
 <option value="Earth">
 <option value="Mars">
 <option value="Jupiter">
 <option value="Saturn">
 <option value="Uranus">
 <option value="Neptune">
</datalist>

It even works on input type="color", which is pretty cool!

The most common use case is as an autocomplete widget. That’s how I’m using it over on The Session, where the datalist is updated via Ajax every time the input is updated.

But let’s stick with a simple example, like the list of planets above. Suppose the user types “jup” …the datalist will show “Jupiter” as an option. The user can click on that option to automatically complete their input.

It would be handy if you could automatically submit the form when the user chooses a datalist option like this.

Well, tough luck.

The datalist element emits no events. There’s no way of telling if it has been clicked. This is something I’ve been trying to find a workaround for.

I got my hopes up when I read Amber’s excellent article about document.activeElement. But no, the focus stays on the input when the user clicks on an option in a datalist.

So if I can’t detect whether a datalist has been used, this best I can do is try to infer it. I know it’s not exactly the same thing, and it won’t be as reliable as true detection, but here’s my logic:

• Keep track of the character count in the input element.
• Every time the input is updated in any way, check the current character count against the last character count.
• If the difference is greater than one, something interesting happened! Maybe the user pasted a value in …or maybe they used the datalist.
• Loop through each of the options in the datalist.
• If there’s an exact match with the current value of the input element, chances are the user chose that option from the datalist.
• So submit the form!

Here’s how that translates into DOM scripting code:

document.querySelectorAll('input[list]').forEach( function (formfield) {
  var datalist = document.getElementById(formfield.getAttribute('list'));
  var lastlength = formfield.value.length;
  var checkInputValue = function (inputValue) {
    if (inputValue.length - lastlength > 1) {
      datalist.querySelectorAll('option').forEach( function (item) {
        if (item.value === inputValue) {
          formfield.form.submit();
        }
      });
    }
    lastlength = inputValue.length;
  };
  formfield.addEventListener('input', function () {
    checkInputValue(this.value);
  }, false);
});

I’ve made a gist with some added feature detection and mustard-cutting at the start. You should be able to drop it into just about any page that’s using datalist. It works even if the options in the datalist are dynamically updated, like the example on The Session.

It’s not foolproof. The inference relies on the difference between what was previously typed and what’s autocompleted to be more than one character. So in the planets example, if someone has type “Jupite” and then they choose “Jupiter” from the datalist, the form won’t automatically submit.

But still, I reckon it covers most common use cases. And like the datalist element itself, you can consider this functionality a progressive enhancement.

I made the website for the Clearleft podcast last week. The design is mostly lifted straight from the rest of the Clearleft website. The main difference is the masthead. If the browser window is wide enough, there’s a background image on the right hand side.

I mostly added that because I felt like the design was a bit imbalanced without something there. On the home page, it’s a picture of me. Kind of cheesy. But the image can be swapped out. On other pages, there are different photos. All it takes is a different class name on that masthead.

I thought about having the image be completely random (and I still might end up doing this). I’d need to use a bit of JavaScript to choose a class name at random from a list of possible values. Something like this:

var names = ['jeremy','katie','rich','helen','trys','chris'];
var name = names[Math.floor(Math.random() * names.length)];
document.querySelector('.masthead').classList.add(name);

(You could paste that into the dev tools console to see it in action on the podcast site.)

Then I read something completely unrelated. Cassie wrote a fantastic article on her site called Making lil’ me - part 1. In it, she describes how she made the mouse-triggered animation of her avatar in the footer of her home page.

It’s such a well-written technical article. She explains the logic of what she’s doing, and translates that logic into code. Then, after walking you through the native code, she shows how you could use the Greeksock library to achieve the same effect. That’s the way to do it! Instead of saying, “Here’s a library that will save you time—don’t worry about how it works!”, she’s saying “Here’s it works without a library; here’s how it works with a library; now you can make an informed choice about what to use.” It’s a very empowering approach.

Anyway, in the article, Cassie demonstrates how you can use custom properties as a bridge between JavaScript and CSS. JavaScript reads the mouse position and updates some custom properties accordingly. Those same custom properties are used in CSS for positioning. Voila! Now you’ve got the position of an element responding to mouse movements.

That’s what made me think of the code snippet I wrote above to update a class name from JavaScript. I automatically thought of updating a class name because, frankly, that’s how I’ve always done it. I’d say about 90% of the DOM scripting I’ve ever done involves toggling the presence of class values: accordions, fly-out menus, tool-tips, and other progressive disclosure patterns.

That’s fine. But really, I should try to avoid touching the DOM at all. It can have performance implications, possibly triggering unnecessary repaints and reflows.

Now with custom properties, there’s a direct line of communication between JavaScript and CSS. No need to use the HTML as a courier.

This made me realise that I need to be aware of automatically reaching for a solution just because that’s the way I’ve done something in the past. I should step back and think about the more efficient solutions that are possible now.

It also made me realise that “CSS variables” is a very limiting way of thinking about custom properties. The fact that they can be updated in real time—in CSS or JavaScript—makes them much more powerful than, say, Sass variables (which are more like constants).

But I too have been guilty of underselling them. I almost always refer to them as “CSS custom properties” …but a lot of their potential comes from the fact that they’re not confined to CSS. From now on, I’m going to try calling them custom properties, without any qualification.

Day two ended with a bit of a cliffhanger as I had the students mark up a document, but not yet style it. In the morning of day three, the styling began.

Rather than just treat “styling” as one big monolithic task, I broke it down into typography, colour, negative space, and so on. We time-boxed each one of those parts of the visual design. So everyone got, say, fifteen minutes to write styles relating to font families and sizes, then another fifteen minutes to write styles for colours and background colours. Bit by bit, the styles were layered on.

When it came to layout, we closed the laptops and returned to paper. Everyone did a quick round of 6-up sketching so that there was plenty of fast iteration on layout ideas. That was followed by some critique and dot-voting of the sketches.

Rather than diving into the CSS for layout—which can get quite complex—I instead walked through the approach for layout; namely putting all your layout styles inside media queries. To explain media queries, I first explained media types and then introduced the query part.

I felt pretty confident that I could skip over the nitty-gritty of media queries and cross-device layout because the next masterclass that will be taught at the New Digital School will be a week of responsive design, taught by Vitaly. I just gave them a taster—Vitaly can dive deeper.

By lunch time, I felt that we had covered CSS pretty well. After lunch it was time for the really challenging part: JavaScript.

The reason why I think JavaScript is challenging is that it’s inherently more complex than HTML or CSS. Those are declarative languages with fairly basic concepts at heart (elements, attributes, selectors, etc.), whereas an imperative language like JavaScript means entering the territory of logic, loops, variables, arrays, objects, and so on. I really didn’t want to get stuck in the weeds with that stuff.

I focused on the combination of JavaScript and the Document Object Model as a way of manipulating the HTML and CSS that’s already inside a browser. A lot of that boils down to this pattern:

When (some event happens), then (take this action).

We brainstormed some examples of this e.g. “When the user submits a form, then show a modal dialogue with an acknowledgement.” I then encouraged them to write a script …but I don’t mean a script in the JavaScript sense; I mean a script in the screenwriting or theatre sense. Line by line, write out each step that you want to accomplish. Once you’ve done that, translate each line of your English (or Portuguese) script into JavaScript.

I did quick demo as a proof of concept (which, much to my surprise, actually worked first time), but I was at pains to point out that they didn’t need to remember the syntax or vocabulary of the script; it was much more important to have a clear understanding of the thinking behind it.

With the remaining time left in the day, we ran through the many browser APIs available to JavaScript, from the relatively simple—like querySelector and Ajax—right up to the latest device APIs. I think I got the message across that, using JavaScript, there’s practically no limit to what you can do on the web these days …but the trick is to use that power responsibly.

At this point, we’ve had three days and we’ve covered three layers of web technologies: HTML, CSS, and JavaScript. Tomorrow we’ll take a step back from the nitty-gritty of the code. It’s going to be all about how to plan and think about building for the web before a single line of code gets written.