svg-loader: A Different Way to Work With External SVG

SVGs are awesome: they are small, look sharp on any scale, and can be customized without creating a separate file. However, there is something I feel is missing in web standards today: a way to include them as an external file that also retains the format’s customization powers.

For instance, let’s say you want to use your website’s logo stored as web-logo.svg. You can do:

<img src="/images/logo.svg" />

That’s fine if your logo is going to look the same everywhere. But in many cases, you have 2-3 variations of the same logo. Slack, for example, has two versions.

Even the colors in the main logo are slightly different.

If we had a way to customize fill color of our logo above, we could pass any arbitrary color to render all the variations.

Take the case of icons, too. You wouldn’t want to do something like this, would you?

<img src="/icons/heart-blue.svg" />
<img src="/icons/heart-red.svg" />

Load external SVGs as inline elements

To address this, I have created a library called svg-loader. Simply put, it fetches the SVG files via XHR and loads them as inline elements, allowing you to customize the properties like fill and stroke, just like inline SVGs.

For example, I have a logo on my side-project, SVGBox. Instead of creating a different file for every variation, I can have one file and customize the fill color:

I used data-src to set the URL of SVG file. The fill attribute overrides fill of the original SVG file.

To use the library, the only thing I have to ensure is that files being served have appropriate CORS headers for XHRs to succeed. The library also caches the files locally, making the subsequent much faster. Even for the first load, the performance is comparable to using <img> tags.

This concept isn’t new. svg-inject does something similar. However, svg-loader is easier to use as we only have to include the library somewhere in your code (either via a <script> tag, or in the JavaScript bundle). No extra code is needed.

Dynamically-added elements and change in attributes are also handled automatically, which ensures that it works with all web frameworks. Here’s an example in React:

But why?

This approach may feel unorthodox because it introduces a JavaScript dependency and there are already multiple ways to use SVGs, including inline and from external sources. But there’s a good case for using SVGs this way. Let’s examine them by answering the common questions.

Can we not just inline SVG ourselves?

Inlining is the simplest way to use SVGs. Just copy and paste the SVG code in the HTML. That’s what svg-loader is ultimately doing. So, why add the extra steps to load a SVG file from somewhere else? There are two major reasons:

1. Inline SVGs make the code verbose: SVGs can be anywhere from a few lines to a few hundred. Inline SVGs can work well if what you need is just a couple of icons and they are all tiny. But it becomes a major pain if they are sizeable or many, because then, they become long strings of text in code that isn’t “business logic.” The code becomes hard to parse.
   
   It’s the same thing as preferring an external stylesheet over a <style> tag or using images instead of data URIs. It’s no wonder that in React codebases, the preferred approach is to use SVG as a separate component, rather than define it as a part of JSX.

2. External SVGs are much more convenient: Copying and pasting often does the job, but external SVGs can be really convenient. Say you’re experimenting with which icon to use in your app. If you’re using inline SVGs, that means going back and forth to get the SVG code. But with external SVGs, you only have to know the name of the file.
   
   Take a look at this example. One of the most extensive icon repository on GitHub is Material Design Icons. With svg-loader and unpkg, we can start using any of 5,000+ icons right away.

Isn’t it inefficient to trigger an HTTP request for every SVG versus making a sprite?

Not really. With HTTP2, the cost of making an HTTP request has become less relevant. Yes, there are still benefits of bundling (e.g., better compression), but for non-blocking resources and XHRs, the pros are almost non-existent in real-world scenarios.

Here’s a Pen loading 50 icons in a similar fashion as above. (Open in incognito mode as the files are cached by default):

What about <use> tag (SVG symbols)?

SVG symbols separate the definition of the SVG file from its use. Instead of defining the SVG everywhere, we can have something like this:

<svg>
  <use xlink:href="#heart-icon" />
</svg>

The problem is that none of the browsers support using symbols files hosted on a third-party domain. Therefore, we can’t do something like this:

<svg>
  <use xlink:href="https://icons.com/symbols.svg#heart-icon" />
</svg>

Safari doesn’t even support symbols files hosted on the same domain.

Can we not use a build tool that inlines the SVGs?

I couldn’t find an obvious way to fetch SVGs from a URL and inline them in common bundlers, like webpack and Grunt, although they exist for inlining SVG files stored locally. Even if a plugin that does this exists, setting up bundlers isn’t exactly straightforward. In fact, I often avoid using them until the project has reached acertain level of complexity. We must also realize that a majority of the internet is alien to things like webpack and React. Simple scripts can have a much wider appeal.

What about the <object> tag?

The <object> tag is a native way to include external SVG files that work across all the browsers.:

<object data="https://unpkg.com/mdi-svg@2.2.43/svg/access-point-network.svg" width="32" height="32"></object>

However, the drawback is we’re unable to customize the SVG’s attributes unless it’s hosted on the same domain (and the <object> tag doesn’t respect CORS headers). Even if the file is hosted on the same domain, we’d require JavaScript to manipulate the fill, like this:

<object data="https://unpkg.com/mdi-svg@2.2.43/svg/access-point-network.svg" width="32" height="32" onload="this.contentDocument.querySelector('svg').fill = 'red'"></object>

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In short, using external SVG files this way makes it ultra-convenient to use icons and other SVG assets. As covered earlier, with unpkg, we can use any icon on GitHub without needing extra code. We can avoid creating a pipeline in a bundler to process SVG files or a component for every icon, and just host the icons on a CDN.

Loading SVG files this way packs a lot of benefits with very little cost.

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