Function packageExportsResolve

lib/internal/modules/esm/resolve.js:589–664

* Resolves the exports of a package. * @param {URL} packageJSONUrl - The URL of the package.json file. * @param {string} packageSubpath - The subpath of the package to resolve. * @param {import('internal/modules/esm/package_config.js').PackageConfig} packageConfig - The package metadata. * @para

(
  packageJSONUrl, packageSubpath, packageConfig, base, conditions)

 * @returns {URL} - The resolved package target.
 */
function packageExportsResolve(
  packageJSONUrl, packageSubpath, packageConfig, base, conditions) {
  let { exports } = packageConfig;
  if (isConditionalExportsMainSugar(exports, packageJSONUrl, base)) {
    exports = { '.': exports };
  }

  if (ObjectPrototypeHasOwnProperty(exports, packageSubpath) &&
      !StringPrototypeIncludes(packageSubpath, '*') &&
      !StringPrototypeEndsWith(packageSubpath, '/')) {
    const target = exports[packageSubpath];
    const resolveResult = resolvePackageTarget(
      packageJSONUrl, target, '', packageSubpath, base, false, false, false,
      conditions,
    );

    if (resolveResult == null) {
      throw exportsNotFound(packageSubpath, packageJSONUrl, base);
    }

    return resolveResult;
  }

  let bestMatch = '';
  let bestMatchSubpath;
  const keys = ObjectGetOwnPropertyNames(exports);
  for (let i = 0; i < keys.length; i++) {
    const key = keys[i];
    const patternIndex = StringPrototypeIndexOf(key, '*');
    if (patternIndex !== -1 &&
        StringPrototypeStartsWith(packageSubpath,
                                  StringPrototypeSlice(key, 0, patternIndex))) {
      // When this reaches EOL, this can throw at the top of the whole function:
      //
      // if (StringPrototypeEndsWith(packageSubpath, '/'))
      //   throwInvalidSubpath(packageSubpath)
      //
      // To match "imports" and the spec.
      if (StringPrototypeEndsWith(packageSubpath, '/')) {
        emitTrailingSlashPatternDeprecation(packageSubpath, packageJSONUrl,
                                            base);
      }
      const patternTrailer = StringPrototypeSlice(key, patternIndex + 1);
      if (packageSubpath.length >= key.length &&
          StringPrototypeEndsWith(packageSubpath, patternTrailer) &&
          patternKeyCompare(bestMatch, key) === 1 &&
          StringPrototypeLastIndexOf(key, '*') === patternIndex) {
        bestMatch = key;
        bestMatchSubpath = StringPrototypeSlice(
          packageSubpath, patternIndex,
          packageSubpath.length - patternTrailer.length);
      }
    }
  }

  if (bestMatch) {
    const target = exports[bestMatch];
    const resolveResult = resolvePackageTarget(