Choosing your Iconography Approach

At the beginning of every web app's development there is the question of iconography. Which icon library do we use? There's lots to choose from: Font Awesome, Fort Awesome, The Noun Project, Material Design Icons, IcoMoon. Generally this choice is up to the designer (if you have one), but as a developer your choice is going to be between using SVG's as icons or Icon fonts. There are a number of pros and cons to SVGs vs Icon fonts that you can find better articles on such as this one. Here's my quick comparison:

SVG Pros:

• SVGs are generally sharper than fonts.
• You are able to specifically pick out and download only the SVGs you want.
• Aligning SVGs is simpler and more predictable because they aren't susceptible to weird font rules such as line height which can add unwanted white space.

SVG Cons:

• Coloring external SVGs can't be done in CSS in a way that's supported in all browsers.

Icon Font Pros:

• Can be colored easily by setting the containing elements 'color' property.

Icon Font Cons:

• While the font is loading up, or if it fails to load, you will see squares like this □ or the ligature of the icon. E.g., you will see the text 'get_app' where the icon should appear.
• Fonts Icons can be trickier to align due to font rules applied to them (mentioned above).
• More difficult to hide from screen readers.

With that brief comparison, it's up to you to decide but I'm going with SVG icons, at least for the rest of this article ;)

Inline SVGs vs External SVGs

Inline SVGs, where the SVG definition is part of the html document, versus External SVGs is the next choice to make.

Mostly this choice comes down to your school of thought on iconography: is iconography part of the style or theme of your web application, aimed to be fully controlled by CSS? Or is iconography a part of the web app's makeup, meaning your html has additional markup just to support icons?

If your school of thought is the former, then congratulations you've made the right choice! Or at least you have from a purists point of view, and definitely if you plan on treating the theme of your web application as a separated concern.

Inline SVGs are still great in the sense that you get the flexibility to use CSS to select and color their elements. Or that they can be animated, but a lot of iconography design on the web today is static and monochrome. If you don't need multicolored, animated icons then you don't need to pollute your HTML with extra inline SVG markup and blur the lines between theme and content structure.

Working with External SVG Icons

Generally the best way to work with SVG Icons is to load them in as background images. This way screen readers will avoid them and we don't need to add extra ARIA attributes to say that they're presentation only.

Why are icons presentation only you say? Well an icon itself doesn't have any meaning to a screenreader. It's something that's meant to convey [extra] meaning to a sighted user in a shorthand way without having to consume precious screen real estate with text. So it's useful to have on a button for example, but that button should already have ARIA attributes to describe its meaning.

SVG Icon as a Background Image

For things like buttons that we're adding SVG icons to, we'll start by setting up a reusable mixin that takes as an argument the path to the icon, and the size of the icon (assuming square dimensions). This mixin will cover all of the properties we'll typically apply to every icon:

@mixin createIconStyle($path-to-svg, $icon-size) {
  background-image: url('~/../src/#{$path-to-svg}');
  background-repeat: no-repeat;
  background-size: $icon-size auto;
  background-position: center;
  height: $icon-size;
  width: $icon-size;
}

Then we can setup a specific css class for an icon using that mixin:

.download-icon {
  @include createIconStyle('/assets/baseline-get_app-24px.svg', 2rem)
}

Note: My example is using webpack which is why it has the weird '~/..' prepended to the icon path.

Now we're free to add this style class to a download button:

<button class="btn btn-primary download-icon" aria-label="Download the thing"></button>

The download button with an icon. Note: I changed my icon to white for this example because the default black on blue looked bad.

Data URLs for Icons

Data URLs are a nice way to bundle your CSS and icons together into the same HTTP request, though there are some good and some vague reasons why this is bad. If handled properly, this can still be a good thing. Especially if you're not using HTTP/2 yet. The main concern is to avoid duplicate data URLs otherwise it can easily bloat your CSS assets fast.

With Sass we can avoid this duplication pretty easily with inheritance. Let's say we want to make a .download-icon-large which is twice as big as the original, then we just inherit the original and override its properties. It's possible to make a mixin of this if it's a common enough occurrence:

@mixin overrideIconSize($extends-class, $icon-size) {
  @extend .#{$extends-class};
  background-size: $icon-size auto;
  height: $icon-size;
  width: $icon-size;
}

.download-icon-large {
  @include overrideIconSize(download-icon, 3rem);
}

This will result in CSS which only includes that data URL once:

.download-icon, .download-icon-large {
  background-image: url('data:image/svg+xml;utf8,<svg ...> ... </svg>')
}

SVG Icon as a Side Image

A popular use for icons is to put them beside some text for a link or a button to give a bit more of a hint to what will happen when it's clicked. Some examples might include a down arrow beside a menu item to hint that it will expand into a submenu. Or a download icon beside the link to a file to hint that it will download instead of open.

These are situations where it's common for developers to add extra markup, usually in the form of an <i> tag or worse an <img> tag. Yuck! Let's keep it all in the CSS please! Remember icons are presentation only, no need for extra markup in our content. That's also not the purpose of an <i> tag and <img> tags download images regardless of visibility which is inefficient, and looks bad with its display of the browser's broken image icon if the download fails.

So without adding extra markup, the solution is to use a pseudo element. Either before or after will do. Which you choose depends on the position of the icon (before for icon on the left, after for icon on the right) but it doesn't matter since position can be controlled in other ways.

For this example, let's say we have a download link with the download icon to the right of it like this:

Expanding on the .download-icon example above, let's create a Sass mixin to create a pseudo element that inherits from the .download-icon:

@mixin existingIconAfter($extends-class, $icon-size) {
  display: inline-flex;
  align-items: center;
  &:after {
    @extend .#{$extends-class};
    vertical-align: middle;
    display: inline-block;
    background-size: $icon-size auto;
    height: $icon-size;
    width: $icon-size;
    content: '';
  }
}

We set the display property to inline-flex and align-items to center so that we can take advantage of Flexbox to vertically align the icon next to the text

Next we create a new class using this mixin and the existing .download-icon class:

.download-icon-after {
  @include existingIconAfter(download-icon, 1.5rem);
}

Then we can add setup our download link:

<a href="..." class="download-icon-after">
  <span>Download</span>
</a>

What's with this <span> tag wrapping the 'Download' text? In this example it's for positioning. On some browsers Flexbox won't recognize text as an item to apply positioning and alignment to. Doesn't this go against "don't add extra markup for icons" approach we're trying to achieve? Maybe, but regardless we'd still want a way to apply styling rules to the separate elements that ultimately make up this link anyways so we can use that span to target the text portion of the link. For example, where horizontal space is limited, we may want to apply rules such that our text will wrap without wrapping the icon too.

If we had a separate theme in our webapp we'd be able to have different looks for this link such as flanking the text with icons on both sides, or removing the icons completely without having to change the structure of the html.

Coloring External SVG Icons using CSS Mask

Applying color to External SVG Icons is unfortunately its weak point depending on your needs. If you don't need to support Internet Explorer, then there's a great solution here using CSS mask which we'll follow. If this doesn't work for you, then one option might be to just create different color variants of the icon SVG files by opening them up and changing their fill color and saving them, or some automated variant of this.

Back to the CSS mask option. The gist of it is that a mask decides the shape of an element, and the only visible parts of that element are inside that mask shape. So if we set an element's background color to blue, and apply a star shaped mask to it then we end up with a blue star. Unfortunately, because the rest of the element outside the star became invisible we lose the elements important details. This means we can't use an SVG mask as a direct replacement for a background image on say a button because the intended outline, background, hover, etc, whatever falls outside the mask shape is invisible. That's no good.

We can solve this using pseudo elements. If we want a star shape icon on a button, we can apply the mask to a pseudo element within the button instead of on the button itself.

Similar to how we have the createIconStyle mixin above, we can start out with a createMaskStyle

@mixin createMaskStyle($path-to-svg, $icon-size) {
  mask: url('~/../src/#{$path-to-svg}');
  mask-repeat: no-repeat;
  mask-size: $icon-size auto;
  mask-position: center;
  height: $icon-size;
  width: $icon-size;
}

And create a css class leveraging that mixin

.download-mask {
  @include createMaskStyle('/assets/baseline-get_app-24px.svg', 2rem)
}

But, like we talked about, we usually don't want to apply a style like this directly to an element. We want to apply it to a pseudo element. Similar to our createIconAfter mixin we will create another mixin to leverage this style class:

@mixin existingMaskAfter($extends-class, $icon-size) {
  display: inline-flex;
  align-items: center;
  &:after {
    @extend .#{$extends-class};
    vertical-align: middle;
    display: inline-block;
    mask-size: $icon-size auto;
    height: $icon-size;
    width: $icon-size;
    content: '';
  }
}

Then we can leverage that mixin to create style classes we can apply to any element we want to have apply this pseudo element to (and maybe readjust its size if we want):

.download-mask-after {
  @include existingMaskAfter(download-mask, 1.5rem);
}

Now you can add an icon to a button like so:

<button class="download-mask-after" aria-label="Download Button"></button>

But wait... I don't see an icon! That's because the pseudo element has nothing to show, so it looks invisible. If we give the pseudo element some color, the icon appears:

button.download-mask-after:after {
  background-color: red;
}

Now we're coloring SVG icons using CSS!

Hurray we have a red download icon to make our eyes sore!

SVG Sprites

In the Data URLs section above we talked about using data URLs as a way to minimize http requests, but that it has drawbacks such as needing to find ways to reduce data URL duplication. If you want to use the CSS Mask technique mentioned above to color your icons, and you have an autoprefixer, then chances are you're going get duplicate data URLs anyways since for every mask property with a data URL there will be at least a -webkit-mask property with the same data URL. An alternative that also helps minimize http requests is to use SVG Sprites.

SVG Sprites is just delivering all of your SVG icons in a single SVG file. Unlike traditional sprite files where you need to know the position of the image inside the file and do some magic to align background positioning over that image, with SVG sprites you can simply reference the image through the URL by its identifier.

For example, I've created a 'sprites.svg' file and inside of it I have, among other icons, my 'getapp' (download) icon which is identified by the name 'getapp' and referenced as a URL fragment like so:

.download-mask-sprite {
  @include createMaskStyle('/assets/sprites.svg#getapp', 2rem)
}

There is some trickery around getting the sprites.svg structured to work for this purpose. Here's an example:

<svg version="1.1"
  xmlns="http://www.w3.org/2000/svg"
  xmlns:xlink="http://www.w3.org/1999/xlink" class="sprites">

  <defs>
    <style>
    svg.sprites {
      display: inline;
    }
    svg {
      display: none;
    }
    svg:target {
      display: inline;
    }
    </style>
  </defs>

  <!-- Here I've pasted in the original SVG, and wrapped it's path elements in a g tag-->
  <svg viewBox="0 0 24 24" id="getapp">
    <g>
      <path d="..."></path>
      <path d="..." fill="none"></path>
    </g>
  </svg>

  <!-- Another SVG in the same file referenced via #setttings URL fragment -->
  <svg viewBox="0 0 20 20" id="settings">
    <g>
      <path fill="none" d="..."></path>
      <path d="..."></path>
    </g>
  </svg>
</svg>

You can read more about it in this article

From here it's up to you to decide how you want to incorporate this into your project. Do you build the sprite file yourself? Alternatively you can use a command line tool, like svg-sprite, to build the sprite file for you. Another option is you can try to make it a part of your project's build.

Coloring SVG Sprites

If the CSS Mask option is not for you then you can change the fill color of the icons inside the sprite file. We can gain an efficiency here where each icon (or rather its paths) is only defined once and then can be referenced multiple times taking advantage of SVG's <use> tag and applying different fill colors.

First all of the icon definitions (the <g> tags) can be moved into the <defs> section of the SVG and given identifiers. Then all of the different color variants of each icon are created using <svg> tags with <use> tags inside them and something to distinguish their color in a CSS selector like a CSS class name. Finally we can use CSS inside the <defs> section to set the fill color on the icons matching that selector.

Here's an iteration on the previous example:

<svg version="1.1"
  xmlns="http://www.w3.org/2000/svg"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  class="sprites">

  <defs>
    <style>
    svg.sprites {
      display: inline;
    }
    svg {
      display: none;
    }
    svg:target {
      display: inline;
    }

    <!-- Make SVGs with 'blue' classnames blue -->
    svg.blue use {
      fill: blue;
    }

    </style>

    <!-- Icon definitions -->
    <g id="getapp_icon">
      <path d="..."></path>
      <path d="..." fill="none"></path>
    </g>

    <g id="settings_icon">
      <path fill="none" d="..."></path>
      <path d="..."></path>
    </g>

  </defs>

  <svg viewBox="0 0 24 24" id="getapp">
    <use xlink:href="#getapp_icon"/>
  </svg>

  <svg viewBox="0 0 20 20" id="settings">
    <use xlink:href="#settings_icon"/>
  </svg>

  <!-- Referenced via #getapp_blue. Will display a blue version of the #getapp icon -->
  <svg viewBox="0 0 24 24" class="blue" id="getapp_blue">
    <use xlink:href="#getapp_icon"/>
  </svg>

  <svg viewBox="0 0 20 20" class="blue" id="settings_blue">
    <use xlink:href="#settings_icon"/>
  </svg>

</svg>

Wrap up

There are a number of approaches to handling iconography in your web application, and even more reasons to choose different approaches (fonts or SVGs, inlined or external, data URLs or sprites, etc.). It all depends on your tastes, technical limitations and capabilities. The aim of this post is to guide you down a specific path of using SVG icons and outline reasons you might want to do it that way.