See https://blockprotocol.org/docs/developing-blocks

TL;DR: Run npx create-block-app [your-block-name]

1. Change into the folder: cd packages/hash/blocks/<name>

2. Write a React component starting in App.tsx. To test it during development:

   • edit src/webpack-dev-server.js to give your component some props to test with
   • run the dev server with yarn start

3. When finished, run yarn build, which:

   • Bundles the component, without React, into a single source file
   • Generates a JSON schema from the AppProps type representing the data interface with the block
   • Generates a block-metadata.json file which:
     • points to the schema and source files
     • brings in metadata from package.json, such as the block name and description
     • additional brings in anything in the blockprotocol object in package.json, e.g.
       • displayName: a friendly display name
       • examples: an array of example data structures your block would accept and use
       • image: a preview image showing your block in action
       • icon: an icon to be associated with your block
     • lists the externals - libraries the block expects the host app to provide (React, unless modified)
   • Once uploaded to a remote folder, embedding applications can access block-metadata.json to load a block and its schema. This file is documented in full here.

N.B.

• The JSON schema generation assumes AppProps is the name of the type for the entry component's properties. If you change this name, update the schema script in package.json
• JSON schema offers more validations than TypeScript - TODO a way of storing these (e.g maxLength) in an extra config file somewhere that doesn't involve manually editing the output schema file each time

You can try out your block in an example embedding application:

1. Clone the example application, HASH, from its repository.

2. Follow the instructions in its README to set up and run HASH.

3. In a new terminal, run yarn serve in your block's folder). Your block dist is now available at http://localhost:5000.

4. In the HASH frontend (once signed in), click on the context menu next to any block on a page. Paste http://localhost:5000 into the ‘load block from URL’ input.

5. Your block should load in its default state. You can now test its functionality, and refresh the page to see how any changes you made persist.

Head over to blockprotocol.org to read instructions on publishing your block.

The Block Component is self contained with all of its dependencies bundled with webpack. Any dependencies that will be provided by the embedding app should be marked as externals in the webpack.config.js, added to devDependencies in package.json so they're available during development, and in peerDependencies if the component is to be made available as a library for importing via npm.

In this example, react is added to externals in webpack.config.js. It will not be included in the bundle. The version in the embedding application must at least provide the functionality that the block expects the library to have, or else there will be obvious difficulties. TODO: Add external library expected versions to block-metadata.json

module.exports = {
  externals: {
    react: "react",
  },
};

There are a few important files, one set is used for the bundle, another set for local development.

• src/index.js - Entrypoint of the Block Component. The component needs to be the default export.
• src/webpack-dev-server.js - Entrypoint for yarn dev. This is only used for development and will not be included in the final bundle.
• src/index.html - HTML for yarn dev. This is only used for development and will not be included in the final bundle.
• variants.json - Defines named presets of block properties to be presented as separate or at least related block-types to the end-user.

The component can be debugged locally by first starting yarn dev.

npm run start

Now (using VS Code), go to the Debug tab, select "Launch Chrome" and start the debugger (F5).

You should now be able to set breakpoints and step through the code.

This template adapted (quite heavily now) from https://github.com/Paciolan/remote-component-starter