Svelte Image
Svelte image is a preprocessor which automates image optimization using sharp.
It parses your img tags, optimizes or inlines them and replaces src accordingly. (External images are not optimized.)
Image component enables lazyloading and serving multiple sizes via srcset.
This package is heavily inspired by gatsby image.
Kudos to @jkdoshi for great video tutorial to Svelte Image.
Installation
yarn add svelte-image -D
svelte-image needs to be added as dev dependency as Svelte requires original component source
In your rollup.config.js add image to preprocess section:
import image from "svelte-image";
svelte({
preprocess: {
...image(),
}
})
And have fun!
<script>
import Image from "svelte-image";
</script>
<Image src="fuji.jpg">
Will generate
<img
src="data:image/png;base64,/9j/2wBDAAYEBQYFBAYG...BwYIChAKCgkJChQODwwQF"
alt="fuji">
<img
alt="fuji"
sizes="(max-width: 1000px) 100vw, 1000px"
srcset="g/400-fuji.jpg 375w, g/800-fuji.jpg 768w, g/1200-fuji.jpg 1024w"
>
Image path
Please note that the library works only with relative paths in Sapper at the moment.
<Image src="images/fuji.jpg"> works whereas <Image src="/images/fuji.jpg"> doesn't.
Svelte + Rollup
To use without Sapper, the generated static/g folder needs to be copied to the public folder. Use rollup-plugin-copy in rollup.config.js:
import svelte from 'rollup-plugin-svelte'
import image from 'svelte-image'
import copy from 'rollup-plugin-copy'
export default {
...
plugins: [
...
svelte({
...
preprocess: {
...image({...})
}
}),
copy({
targets: [{ src: 'static/g', dest: 'public' }],
}),
]
}
Configuration and defaults
Image accepts following configuration object:
const defaults = {
optimizeAll: true, // optimize all images discovered in img tags
// Case insensitive. Only files whose extension exist in this array will be
// processed by the <img> tag (assuming `optimizeAll` above is true). Empty
// the array to allow all extensions to be processed. However, only jpegs and
// pngs are explicitly supported.
imgTagExtensions: ['jpg', 'jpeg', 'png'],
// Same as the above, except that this array applies to the Image Component.
// If the images passed to your image component are unknown, it might be a
// good idea to populate this array.
componentExtensions: [],
inlineBelow: 10000, // inline all images in img tags below 10kb
compressionLevel: 8, // png quality level
quality: 70, // jpeg/webp quality level
tagName: "Image", // default component name
sizes: [400, 800, 1200], // array of sizes for srcset in pixels
// array of screen size breakpoints at which sizes above will be applied
breakpoints: [375, 768, 1024],
outputDir: "g/",
// should be ./static for Sapper and ./public for plain Svelte projects
publicDir: "./static/",
placeholder: "trace", // or "blur",
// WebP options [sharp docs](https://sharp.pixelplumbing.com/en/stable/api-output/#webp)
webpOptions: {
quality: 75,
lossless: false,
force: true
},
webp: true,
// Potrace options for SVG placeholder
trace: {
background: "#fff",
color: "#002fa7",
threshold: 120
}
// Wheter to download and optimize remote images loaded from a url
optimizeRemote: true,
};
Image component props
Standard image tag props.
-
classdefault: "" -
altdefault: "" -
widthdefault: "" -
heightdefault: "" -
cdefault: "" Class string // deprecated in favor ofclass -
wrapperClassdefault: "" Classes passed to Waypoint wrapper -
placeholderClassdefault: "" Classes passed to placeholder -
thresholddefault: 1.0 "A threshold of 1.0 means that when 100% of the target is visible within the element specified by the root option, the callback is invoked." -
lazydefault: true Disables Waypoint.
Following props are filled by preprocessor:
srcdefault: ""srcsetdefault: ""srcsetWebpdefault: ""ratiodefault: "100%"blurdefault: falsesizesdefault: "(max-width: 1000px) 100vw, 1000px"
Features
- Generate and add responsive images
- Set base64 placeholder
- Optimize normal images using
imgtag - Image lazy loading
- Optional SVG trace placeholder
- Support WebP
- Optimize background or whatever images found in CSS
- Resolve imported images (only works with string pathnames at the moment)
Development
Run yarn && yarn dev in the /dev directory. This is the source code of demo homepage.
Testing
You can test the preprocessor via yarn test. We are using Jest for that, so you can also pass a --watch flag to test while developing.
Currently, the best way to test the Svelte component is by using it in a separate project and using yarn/npm link. The dev directory tends to have issues keeping in sync with changes to the src in the root of the repo.