Inconsistent viewBox attribute in `<svg/>` elements

[delilahw]

What version of astro-icon are you using?

v1.1.2

Astro Info

Astro                    v4.16.10
Node                     v18.20.3
System                   Linux (x64)
Package Manager          unknown
Output                   static
Adapter                  none
Integrations             astro-icon

If this issue only occurs in one browser, which browser is a problem?

No response

Describe the Bug

Hi! Thank you all for your work on this library, it's been super helpful in optimising icons and bringing them to my Astro site. 😇

In #246, the viewBox attribute was moved from <svg/> to <symbol/>. However, for non-inline icons, it appears that this only takes effect on the first occurrence of <Icon/>. Subsequent instances of <Icon/> retain their viewBox attribute, which is inconsistent behaviour.

That is,

{/* Put both of these `<Icon/>` instances, one after another, in the same Astro file: */}

{/* This renders `<svg/>` _without_ a `viewBox` attribute */}
<Icon name="square"/>

{/* This renders `<svg/>` _with_ a `viewBox` attribute */}
<Icon name="square"/>

I suspect the cause to be: includeSymbol: bool determines whether to remove the viewBox attribute. According to the below assignment, it will be false in subsequent usages of <Icon/> because i > 0.

astro-icon/packages/core/components/Icon.astro

Line 39 in 531db17

const includeSymbol = !inline && i === 0;

astro-icon/packages/core/components/Icon.astro

Lines 118 to 124 in 531db17

	const { viewBox } = normalizedProps;
	if (includeSymbol) {
	delete normalizedProps.viewBox;
	}
	---
	<svg {...normalizedProps} data-icon={name}>

What's the expected result?

The behaviour should be consistent. A consumer should be able to specify the same markup (<Icon name="square"/>) and expect them to render <svg/> that behaves the same — it should either omit the viewBox attribute across all instances, or include them across all instances.

Another suggestion is to add some sort of attribute/config to let users decide the viewBox behaviour.

Link to Minimal Reproducible Example

https://stackblitz.com/edit/github-u6hdxa?file=src%2Fpages%2Findex.astro

[alxndrsn]

I think I'm experiencing this - the first <Icon> on a page looks fine, but subsequent instances are invisible unless viewBox is manually removed from the generated <svg> elements in the page source.

[delilahw]

@alxndrsn My current workaround is just pinning it to v1.1.1 for now. Hopefully someone has time to triage this soon =)

[alxndrsn]

@delilahw thanks 🙂

I replaced it with a custom component:

---
import icnA from '../icons/a.svg?raw';
import icnB from '../icons/b.svg?raw';
...

export function htmlFrom(iconName) {
  switch(iconName) { 
    case 'a': return icnA;
    case 'b': return icnB;
    ...
    default: return '<div>missing icon</div>';
  }
}

const { src } = Astro.props;
  
const iconHtml = htmlFrom(src);
---
<Fragment set:html={iconHtml /*eslint-disable-line astro/no-set-html-directive*/}/>

A bit annoying as every icon has to be added to the switch statement, but it gives direct control over what actually happens to the generated markup.

[stramel]

Apologies! I'll get this fixed soon! This stemmed from #212

[stramel]

Investigation

So looking into this further. This is the current functionality in astro@5.0.0-beta.9.

Why this happens

The <symbol> element does not define any intrinsic size—it relies on the viewBox for coordinate scaling but leaves sizing to be explicitly defined by the <svg> tag using the <use> element.

Options to Address It

Option 1: Specify both width and height or size (Current)

Explicitly setting the size on the icon will resolve the lack of sizing.

Option 2: Use CSS

Instead of hardcoding the width and height, you can define them via

<svg>
  <symbol id="icon-star" viewBox="0 0 24 24">
    <path d="M12 2l3.09 6.26L22 9.27l-5 4.87L18.18 22 12 18.27 5.82 22 7 14.14l-5-4.87 6.91-1.01L12 2z" />
  </symbol>
  <use href="#icon-star"></use>
</svg>

<svg class="icon">
  <use href="#icon-star"></use>
</svg>

<style>
  .icon {
    width: 50px;
    height: auto; /* Allows aspect ratio to be maintained */
  }
</style>

In this case:

CSS defines the dimensions, and you can use height: auto to let the aspect ratio control the scaling.

Option 3: Move the viewBox onto <svg>

You can define a viewBox directly on the <svg> element that uses <use>. This approach allows the browser to calculate dimensions based on the viewBox's aspect ratio, even if only one of width or height is specified:

<svg>
  <symbol id="icon-star" viewBox="0 0 24 24">
    <path d="M12 2l3.09 6.26L22 9.27l-5 4.87L18.18 22 12 18.27 5.82 22 7 14.14l-5-4.87 6.91-1.01L12 2z" />
  </symbol>
  <use href="#icon-star"></use>
</svg>

<svg viewBox="0 0 24 24" width="50">
  <use href="#icon-star"></use>
</svg>

Here:

The viewBox on <svg> takes precedence, so the width of 50 ensures proper scaling, and the height is calculated automatically based on the viewBox's aspect ratio.

Option 4: Use a Default Dimension on the <symbol>

Add default width and height attributes to the <symbol> itself. These will be inherited by <use> instances unless overridden.

Summary

We have a few options for direction, we can hopefully find the way that best fits everyone's needs. I will discuss with @natemoo-re and find out the best course of action. This will also impact the experimental Astro SVG Components on v5 beta.

[stramel]

@delilahw @alxndrsn This library is going to be shifting to covering only iconify as we've merged the handling of SVG files primarily to Astro. Would love for you to test it out and provide some initial feedback!

Please try upgrading to astro@^5.0.0-beta.11

You can read the docs about it here: https://5-0-0-beta.docs.astro.build/en/reference/experimental-flags/svg/

You can provide feedback about it here: withastro/roadmap#1035

[fwextensions]

Glad I found this thread, as I was banging my head against the wall trying to figure out why the first instance of an svg icon looked right but subsequent ones didn't. @delilahw's suggestion of pinning to v1.1.1 fixes it, even with Astro v5.1.1.

@stramel keep in mind that the viewBox attribute isn't just about sizing the icon but also positioning it within the bounding box, which is not something you can do with CSS (AFAIK? I'm assuming left and top CSS styles wouldn't affect the svg viewBox).

In my case, I was using an icon that was flush up against the viewBox boundary, and I wanted to add some padding around it in certain cases but not others. I can't remember exactly why, but it seemed only possible (or just easier) to do with the viewBox than trying to add the padding with CSS. Worked great until I blindly updated astro-icon along with other deps when updating to Astro v5.

[delucis]

viewBox attribute isn't just about sizing the icon but also positioning it within the bounding box

Yeah, I also hit this while upgrading to v1. You can’t use preserveAspectRatio for example in the absence of a viewBox:

The aspect ratio of an SVG image is defined by the viewBox attribute. Therefore, if viewBox isn't set, the preserveAspectRatio attribute has no effect on SVG's scaling