.babelrc.js

/**
 * Transform d3 ESM libraries to vendored CommonJS libraries
 *
 * This produces `lib-vendor/d3-<package name>/src` files that have
 * internally consistent references to other d3 packages. It is only meant
 * to be used for the CommonJS import path.
 */
const path = require('path');

module.exports = {
  only: [/node_modules\/(d3-.*|internmap|delaunator|robust-predicates)\/.*\.js/],
  plugins: [
    [
      '@babel/transform-modules-commonjs',
      {
        strict: false,
        allowTopLevelThis: true,
      },
    ],
    [
      'module-resolver',
      {
        // Convert all imports for _other_ d3 dependencies to the relative
        // path in our vendor package.
        resolvePath(sourcePath, currentFile) {
          const d3pattern =
            /^(?<pkg>(d3-[^\/]+|internmap|delaunator|robust-predicates))(?<path>.*)/;
          const match = d3pattern.exec(sourcePath);
          if (match) {
            // We're assuming a common shape of d3 packages:
            // - Only top level imports "d3-<whatever>"
            // - With no path components (like "d3-<whatever>/path/to.js")
            if (match.groups.path) {
              throw new Error(`Unable to process ${sourcePath} import in ${currentFile}`);
            }

            // Get Vendor package path.
            const vendorPkg = ['delaunator', 'robust-predicates'].includes(match.groups.pkg)
              ? path.resolve(__dirname, `./lib-vendor/${match.groups.pkg}/index.js`)
              : path.resolve(__dirname, `./lib-vendor/${match.groups.pkg}/src/index.js`);

            // Derive relative path to vendor lib to have a file like move from:
            // - 'node_modules/d3-interpolate/src/rgb.js'
            // - 'lib-vendor/d3-interpolate/src/rgb.js'
            // and have an import transform like:
            // - `d3-color`
            // - `../../d3-color`
            const currentFileVendor = currentFile.replace(/^node_modules/, 'lib-vendor');
            const relPathToPkg = path
              .relative(path.dirname(currentFileVendor), vendorPkg)
              .replace(/\\/g, '/');

            return relPathToPkg;
          }

          return sourcePath;
        },
      },
    ],
    '@babel/plugin-transform-runtime',
  ],
};