SvelteKit Open Graph Image Generation

Dynamically generate Open Graph images from an HTML+CSS template or Svelte component using fast and efficient conversion from HTML > SVG > PNG. Based on Satori. No headless browser required.

Installation

pnpm install -D @ethercorps/sveltekit-og

Using with Cloudflare Pages or Workers then you have to provide url polyfill by just installing it as devDependency.

pnpm i -D url

Usage

Create a file at /src/routes/og/+server.ts. Alternatively, you can use JavaScript by removing the types from this example.

// src/routes/og/+server.ts
import { ImageResponse } from '@ethercorps/sveltekit-og';
import { RequestHandler } from './$types';

const template = `
 <div tw="bg-gray-50 flex w-full h-full items-center justify-center">
    <div tw="flex flex-col md:flex-row w-full py-12 px-4 md:items-center justify-between p-8">
      <h2 tw="flex flex-col text-3xl sm:text-4xl font-bold tracking-tight text-gray-900 text-left">
        <span>Ready to dive in?</span>
        <span tw="text-indigo-600">Start your free trial today.</span>
      </h2>
      <div tw="mt-8 flex md:mt-0">
        <div tw="flex rounded-md shadow">
          <a href="#" tw="flex items-center justify-center rounded-md border border-transparent bg-indigo-600 px-5 py-3 text-base font-medium text-white">Get started</a>
        </div>
        <div tw="ml-3 flex rounded-md shadow">
          <a href="#" tw="flex items-center justify-center rounded-md border border-transparent bg-white px-5 py-3 text-base font-medium text-indigo-600">Learn more</a>
        </div>
      </div>
    </div>
  </div>
`;

const fontFile = await fetch('https://og-playground.vercel.app/inter-latin-ext-400-normal.woff');
const fontData: ArrayBuffer = await fontFile.arrayBuffer();

export const GET: RequestHandler = async () => {
  return await ImageResponse(template, {
    height: 630,
    width: 1200,
    fonts: [
      {
        name: 'Inter Latin',
        data: fontData,
        weight: 400
      }
    ]
  });
};

Then run npm dev and visit localhost:5173/og to view your generated PNG. Remember that hot module reloading does not work with server routes, so if you change your HTML or CSS, hard refresh the route to see changes.

Example Output

Headers

When run in development, image headers contain cache-control: no-cache, no-store. In production, image headers contain 'cache-control': 'public, immutable, no-transform, max-age=31536000', which caches the image for 1 year. In both cases, the 'content-type': 'image/png' is used.

Styling

Notice that our example uses TailwindCSS classes (e.g. tw="bg-gray-50"). Alternatively, your HTML can contain style attributes using any of the subset of CSS supported by Satori.

Satori supports only a subset of HTML and CSS. For full details, see Satori’s documentation. Notably, Satori only supports flex-based layouts.

Fonts

Satori supports ttf, otf, and woff font formats; woff2 is not supported. To maximize the font parsing speed, ttf or otf are recommended over woff.

By default, @ethercorps/sveltekit-og includes only 'Noto Sans' font. If you need to use other fonts, you can specify them as shown in the example. Notably, you can also import a font file that is stored locally within your project and are not required to use fetch.

Examples

• ImageResponse · source · demo
• componentToImageResponse · source · demo

API Reference

The package exposes an ImageResponse and componentToImageResponse constructors, with the following options available:

import {ImageResponse, componentToImageResponse} from '@ethercorps/sveltekit-og'
import {SvelteComponent} from "svelte";

// ...
ImageResponse(
    element : string,
    options : {
      width ? : number = 1200
      height ? : number = 630,
      backgroundColor ? : string = "#fff"
      fonts ? : {
          name: string,
          data: ArrayBuffer,
          weight: number,
          style: 'normal' | 'italic'
      }[]
      debug ? : boolean = false
      graphemeImages ? : Record<string, string>;
      loadAdditionalAsset ? : (languageCode: string, segment: string) => Promise<SatoriOptions["fonts"] | string | undefined>;
      // Options that will be passed to the HTTP response
      status ? : number = 200
      statusText ? : string
      headers ? : Record<string, string>
    })

componentToImageResponse(
    component : typeof SvelteComponent,
    props : {}, // All export let example inside prop dictionary
    options : {
      width ? : number = 1200
      height ? : number = 630
      fonts ? : {
          name: string,
          data: ArrayBuffer,
          weight: number,
          style: 'normal' | 'italic'
      }[]
      debug ? : boolean = false
      graphemeImages ? : Record<string, string>;
      loadAdditionalAsset ? : (languageCode: string, segment: string) => Promise<SatoriOptions["fonts"] | string | undefined>;
      // Options that will be passed to the HTTP response
      status ? : number = 200
      statusText ? : string
      headers ? : Record<string, string>
    })

Changelog

v1.2.3 Update (Breaking Changes)

Now you have to install dependency by yourself which will make it easier to build for all plateforms.

npm i @resvg/resvg-js

npm i satori

From now on their will be no issues related to build, and soon this library going to have its own documentation.

v1.2.2 Update (Breaking Change)

• We don't provide access to satori from @ethercorps/sveltekit-og.

v1.0.0 Update (Breaking Changes)

Finally, We have added html to react like element like object converter out of the box and with svelte compiler. Now you can use { toReactElement } with "@ethercorps/sveltekit-og" like:

• We have changed to function based instead of class based ImageResponse and componentToImageResponse.
• Removed @resvg/resvg-wasm with @resvg/resvg-js because of internal errors.
• Removed satori-html because now we have toReactElement out of the box with svelte compiler.

  If you find a problem related to undefined a please check vite.config.js and add define: { _a: 'undefined' } in config.

If you find any issue and have suggestion for this project please open a ticket and if you want to contribute please create a new discussion.

Acknowledgements

This project will not be possible without the following projects:

• Satori & @vercel/og
• Noto by Google Fonts
• svg2png-wasm

Authors

• @theetherGit
• @etherCorps

Contributors

• @jasongitmail