Best way to import SVG icons into a Svelte app

Question

I have about 80 custom SVG icons that I'm importing into a Svelte front-end app. Building on https://github.com/sveltejs/template, it's built with Rollup and includes Typescript, Tailwind, and all the modern goodies.

The dilemma is how to add the icons into the app. As SVGs, the icons are short XML text strings that do not exceed 2kB.

Option 1: as image assets

1. Upload all the icons as foo.svg into public/assets/icons.
2. Create a svelte component <Icon type="foo' /> that displays an the icon using <img src="foo.svg>.

This approach means that the icons are not part of the code.

Benefits: icons can be dynamically loaded by frontend code on demand. No need to bundle all icons into app code.

Cons: slow page load if there are a lot of new icons, and the browser has to fetch a dozen 1kB files. Deploying the app as a PWA means we need to manually tell it to cache the icons beforehand.

Option 2: as part of the app build

1. Use something like https://github.com/cristovao-trevisan/svelte-icon or https://github.com/codefeathers/rollup-plugin-svelte-svg to directly import each icon into code: import Home from './icons/home.svg';
2. Create a svelte component that selects the right imported component or SVG string and displays it.

Here, the icons are bundled as text strings with the app itself.

Benefits: Icons are delivered as part of the app bundle. Caching is unnecessary. Possible to dynamically modify some of the icon code e.g. colors, viewBox, etc on load.

Cons: It's unnecessary to include all icons in the app to reduce time to first byte. Can't do bundle splitting, etc. without adding more complexity. Makes the rendering slower because Javascript code needs to first turn a string into an SVG instead of just loading an image.

Questions

• It seems that building icons in tthe app is a better way from this analysis, but have I missed something?
• Does the calculus change if the "icons" are detailed images that are 50-100kB instead of the tiny strings here?

Answer 1

You can just change the file extension to .svelte and import an SVG as a normal component.

Answer 2

The following approach has these advantages:

• One central point to maintain all your icons for your app
• Reduced network requests for fetching SVG icons
• Reusable icons throughout the app without having duplicate svg elements

Have a dedicated Icon.svelte component setup like this:

<script>
    export let name;
    export let width = "1rem";
    export let height = "1rem";
    export let focusable = false;
    let icons = [
        {
          box: 24,
          name: "save",
          svg: `<g stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M19 21H5a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h11l5 5v11a2 2 0 0 1-2 2z"/><path d="M17 21v-8H7v8"/><path d="M7 3v5h8"/></g>`
        },
        {
          box: 32,
          name: "trash",
          svg: `<path d="M12 12h2v12h-2z" /><path d="M18 12h2v12h-2z" /><path d="M4 6v2h2v20a2 2 0 0 0 2 2h16a2 2 0 0 0 2-2V8h2V6zm4 22V8h16v20z" /><path d="M12 2h8v2h-8z" />`
        }
    ];
    let displayIcon = icons.find((e) => e.name === name);
</script>
<svg
  class={$$props.class}
  {focusable}
  {width}
  {height}
  viewBox="0 0 {displayIcon.box} {displayIcon.box}">{@html displayIcon.svg}</svg>

You can then use it like so:

<Icon name="trash" class="this-is-optional" />

Answer 3

another way is to use a symbol defs file (ex: icons.svg) in your public folder. then in your code do something like this :

Icon.svelte

<script>
    export let name;
    export let width = "1.5rem";
    export let height = "1.5rem";
    export let focusable = false;
</script>

<svg class={$$props.class} {focusable} {width} {height}>
    <use href={`/icons.svg#${name}`} />
</svg>

icons.svg

<svg aria-hidden="true" style="position: absolute; width: 0; height: 0; overflow: hidden;" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
    <defs>
        <symbol id="icon-warning" viewBox="0 0 20 20">
            <path d="M19.511 17.98l-8.907-16.632c-0.124-0.215-0.354-0.348-0.604-0.348s-0.481 0.133-0.604 0.348l-8.906 16.632c-0.121 0.211-0.119 0.471 0.005 0.68 0.125 0.211 0.352 0.34 0.598 0.34h17.814c0.245 0 0.474-0.129 0.598-0.34 0.124-0.209 0.126-0.469 0.006-0.68zM11 17h-2v-2h2v2zM11 13.5h-2v-6.5h2v6.5z">
            </path>
        </symbol>
    </defs>
</svg>

App.svelte

<Icon name="icon-warning" />

this way you use one http call to load svg file. and then just use the part you need in markup.

Answer 4

Using like {@html SVG_CODE} for rendering a svg code from another component or variable is a Bad choice . This sometimes gives risk of XSS attack . Specially when the image comes from external source. check : https://github.com/sveltejs/svelte/issues/2545

Svelte doesn't perform any sanitization of the expression inside {@html ...} before it gets inserted into the DOM. In other words, if you use this feature it's critical that you manually escape HTML that comes from sources you don't trust, otherwise you risk exposing your users to XSS attacks.(source)

I think using plugin like rollup-plugin-svelte-svg would be a better choice

1.Install using npm

npm i -D rollup-plugin-svelte-svg

2.Simply call svelteSVG before svelte in your rollup config.

export default {
    
    plugins: [
        svelteSVG({
            // optional SVGO options
            // pass empty object to enable defaults
            svgo: {}
        }),
    ],
    ...
}

3.You can then import svg in your JS thusly:

<script>
    import Logo from "./logo.svg";
</script>

<Logo width=20 />

Or

Open your svg image using text editor, copy all the code and paste in a file name with .svelte extension .

for example , icon.svg file contains :

<svg class="w-6 h-6" fill="currentColor" viewBox="0 0 20 20" xmlns="http://www.w3.org/2000/svg"><path fill-rule="evenodd" d="M14.243 5.757a6 6 0 10-.986 9.284 1 1 0 111.087 1.678A8 8 0 1118 10a3 3 0 01-4.8 2.401A4 4 0 1114 10a1 1 0 102 0c0-1.537-.586-3.07-1.757-4.243zM12 10a2 2 0 10-4 0 2 2 0 004 0z" clip-rule="evenodd"></path></svg>

Copy it in a icon.svelte file

<script></script>
<style></style>
<svg class="w-6 h-6" fill="currentColor" viewBox="0 0 20 20" xmlns="http://www.w3.org/2000/svg"><path fill-rule="evenodd" d="M14.243 5.757a6 6 0 10-.986 9.284 1 1 0 111.087 1.678A8 8 0 1118 10a3 3 0 01-4.8 2.401A4 4 0 1114 10a1 1 0 102 0c0-1.537-.586-3.07-1.757-4.243zM12 10a2 2 0 10-4 0 2 2 0 004 0z" clip-rule="evenodd"></path></svg>

When you want use icon.svelte component

<script>
import Icon from "$lib/icon.svelte"
</script>
<style></style>
<Icon />

If you want you can pass optional class

then in icon.svelte

<script></script>
<style></style>
<svg class="{$$props.class}" fill="currentColor" viewBox="0 0 20 20" xmlns="http://www.w3.org/2000/svg"><path fill-rule="evenodd" d="M14.243 5.757a6 6 0 10-.986 9.284 1 1 0 111.087 1.678A8 8 0 1118 10a3 3 0 01-4.8 2.401A4 4 0 1114 10a1 1 0 102 0c0-1.537-.586-3.07-1.757-4.243zM12 10a2 2 0 10-4 0 2 2 0 004 0z" clip-rule="evenodd"></path></svg>

When you want to call icon.svelte component

<script>
import Icon from "$lib/icon.svelte"
</script>
<style></style>
<Icon class="h-6 w-6" />

Answer 5

A working solution is to hold the SVGs in a separate IconService.js:

export const chevron_down = "<svg xmlns=\"http://www.w3.org/2000/svg\" width=\"24\" height=\"24\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\" class=\"feather feather-chevron-down\"><polyline points=\"6 9 12 15 18 9\"></polyline></svg>";

export const chevron_right = "<svg xmlns=\"http://www.w3.org/2000/svg\" width=\"24\" height=\"24\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\" class=\"feather feather-chevron-right\"><polyline points=\"9 18 15 12 9 6\"></polyline></svg>";

This can easily be imported and used within svelte @html function.

<script>
    import {chevron_down, chevron_right} from 'IconService';
</script>

{@html chevron_down}