react.dev/plugins/gatsby-transformer-home-example-code/gatsby-node.js

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 */

const crypto = require('crypto');
const path = require('path');

const createContentDigest = obj =>
  crypto
    .createHash(`md5`)
    .update(obj)
    .digest(`hex`);

// Store code snippets in GraphQL for the home page examples.
// Snippets will be matched with markdown templates of the same name.
exports.onCreateNode = async ({actions, node, loadNodeContent}) => {
  const {createNode} = actions;
  const {absolutePath, ext, name, relativeDirectory, sourceInstanceName} = node;

  if (
    sourceInstanceName === 'content' &&
    relativeDirectory === 'home/examples' &&
    ext === '.js'
  ) {
    const code = await loadNodeContent(node);
    createNode({
      id: name,
      children: [],
      parent: node.id,
      code,
      mdAbsolutePath: absolutePath.replace(/\.js$/, '.md'),
      internal: {
        type: 'ExampleCode',
        contentDigest: createContentDigest(JSON.stringify(code)),
      },
    });
  }
};