Creating The Feature Queries Manager DevTools Extension

Creating The Feature Queries Manager DevTools Extension

Creating The Feature Queries Manager DevTools Extension

Ire Aderinokun

2018-05-23T12:00:00+02:00
2018-06-05T08:35:40+00:00

Within the past couple of years, several game-changing CSS features have been rolled out to the major browsers. CSS Grid Layout, for example, went from 0 to 80% global support within the span of a few months, making it an incredibly useful and reliable tool in our arsenal. Even though the current support for a feature like CSS Grid Layout is relatively great, not all recent or current browsers support it. This means it’s very likely that you and I will currently be developing for a browser in which it is not supported.

The modern solution to developing for both modern and legacy browsers is feature queries. They allow us to write CSS that is conditional on browser support for a particular feature. Although working with feature queries is almost magical, testing them can be a pain. Unlike media queries, we can’t easily simulate the different states by just resizing the browser. That’s where the Feature Queries Manager comes in, an extension to DevTools to help you easily toggle your feature query conditions. In this article, I will cover how I built this extension, as well as give an introduction to how developer tools extensions are built.

Working With Unsupported CSS

If a property-value pair (e.g. display: grid), is not supported by the browser the page is viewed in, not much happens. Unlike other programming languages, if something is broken or unsupported in CSS, it only affects the broken or unsupported rule, leaving everything else around it intact.

Let’s take, for example, this simple layout:

The layout in a supporting browser
Large preview

We have a header spanning across the top of the page, a main section directly below that to the left, a sidebar to the right, and a footer spanning across the bottom of the page.

Here’s how we could create this layout using CSS Grid:

See the Pen layout-grid by Ire Aderinokun (@ire) on CodePen.

In a supporting browser like Chrome, this works just as we want. But if we were to view this same page in a browser that doesn’t support CSS Grid Layout, this is what we would get:

The layout in an unsupporting browser
Large preview

It is essentially the same as if we had not applied any of the grid-related styles in the first place. This behavior of CSS was always intentional. In the CSS specification, it says:

In some cases, user agents must ignore part of an illegal style sheet, [which means to act] as if it had not been there

Historically, the best way to handle this has been to make use of the cascading nature of CSS. According to the specification, “the last declaration in document order wins.” This means that if there are multiple of the same property being defined within a single declaration block, the latter prevails.

For example, if we have the follow declarations:

body {
  display: flex;
  display: grid;
}

Assuming both Flexbox and Grid are supported in the browser, the latter — display: grid — will prevail. But if Grid is not supported by the browser, then that rule is ignored, and any previous valid and supported rules, in this case display: flex, are used instead.

body {
  display: flex;
  display: grid;
}

Cascading Problems

Using the cascade as a method for progressive enhancement is and has always been incredibly useful. Even today, there is no simpler or better way to handle simple one-liner fallbacks, such as this one for applying a solid colour where the rgba() syntax is not supported.

div {
    background-color: rgb(0,0,0);
    background-color: rgba(0,0,0,0.5);
}

Using the cascade, however, has one major limitation, which comes into play when we have multiple, dependent CSS rules. Let’s again take the layout example. If we were to attempt to use this cascade technique to create a fallback, we would end up with competing CSS rules.

See the Pen layout-both by Ire Aderinokun (@ire) on CodePen.

In the fallback solution, we need to use certain properties such as margins and widths, that aren’t needed and in fact interfere with the “enhanced” Grid version. This makes it difficult to rely on the cascade for more complex progressive enhancement.

Feature Queries To The Rescue!


Source: Smashingmagazine

avatar
  Subscribe  
Notify of