svimg

svimg is an image preprocessing and lazy loading component for Svelte. It consists of:

• A Svelte preprocessor that automatically resizes your images to multiple resolutions in a srcset, creates additional AVIF and WebP versions, and generates blurred placeholder images
• A Svelte component that displays the blurred placeholder and automatically lazy loads the proper resolution image when it comes into view

svimg uses native browser lazy loading with a fallback to IntersectionObserver, and automatically calculates the appropriate sizes attribute. Some other image components do not set a proper sizes attribute, which can cause the browser to download a much larger resolution image than necessary if you are resizing the image with CSS. svimg will also use a literal width if specified to control image preprocessing and only generate the necessary image files for that width.

Getting Started

Installation

Since svimg is an external Svelte component, you'll want to make sure it gets bundled by Svelte during compile by installing it as a dev dependency (or modifying your bundler config to not treat it as an external).

npm install -D svimg

In svelte.config.js, add imagePreprocessor as a preprocessor:

import { vitePreprocess } from '@sveltejs/kit/vite';
import { imagePreprocessor } from 'svimg';

/** @type {import('@sveltejs/kit').Config} */
const config = {
    preprocess: [
        imagePreprocessor({
            inputDir: 'static',
            outputDir: 'static/g',
            webp: true,
            avif: true
        }), 
        vitePreprocess()
    ]
};

export default config;

rollup-plugin-svelte does not yet have support for svelte.config.js, so if you're using it you must pass the options inline. In rollup.config.js, add imagePreprocessor as a preprocessor for rollup-plugin-svelte:

import { imagePreprocessor } from 'svimg';

export default {
    plugins: [
        svelte({
            preprocess: [
                imagePreprocessor({
                    inputDir: 'public',
                    outputDir: 'public/g',
                    webp: true,
                    avif: true
                })
            ]
        })
    ]
};

Usage

Svelte Component

<script>
import Image from 'svimg/Image.svelte';
</script>

<Image src="images/splash.jpg" />

<Image src="images/avatar.jpg" width="150" alt="Avatar" class="blue-border" quality="85" immediate />

The Image component will render a blurred placeholder, a srcset with multiple resolutions, a sizes attribute, and sources of type image/avif with avif images and image/webp with webp images.

Custom Element

svimg is also exposed as a custom element, which means it can be used independently of Svelte with the <s-image> tag.

Usage as a custom element expects that the attributes that would normally be filled in by the Svelte preprocessor (srcset, srcsetavif, srcsetwebp, placeholder) are populated by another method.

Generally, you'd use another tool to create these elements such as rehype-svimg rather than using the custom element directly.

<script>
import 'svimg/s-image';
</script>

<s-image srcset="images/splash-600.jpg 600w, images/splash-1200.jpg 1200w" srcsetavif="images/splash-600.avif 600w, images/splash-1200.avif 1200w" srcsetwebp="images/splash-600.webp 600w, images/splash-1200.webp 1200w" />

Configuration

Component Attributes

The following properties will be automatically populated by the preprocessor:

Preprocessor Options

Built With

• Svelte
• sharp

Authors

• Chris Han - Initial work - xiphux

License

This project is licensed under the ISC License - see the LICENSE.md file for details

Acknowledgements

• Gridsome
• svelte-image