Script that resolves all exports + paths from TS barrel files, meant to be used with babel-transform-imports

barrel-file-info.js

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

const ts = require('typescript');

/**
 * Parses a barrel (index) file, extracts all it's export
 * names and returns an object that maps
 * a import name to the path + some meta infos.
 *
 *
 * Note: this doesn't handle the following cases:
 * ```
 * import {A, B} from './foo';
 *
 * export {A,B}
 *
 * export * as Namespace from './foo';
 * ```
 *
 * The case above is not supported.
 */
const collectExports = (file) => {
  const sourceFile = ts.createSourceFile(
    file,
    fs.readFileSync(file).toString(),
    ts.ScriptTarget.ES2015,
    true,
  );

  const exports = {};
  sourceFile.forEachChild((child) => {
    if (ts.isExportDeclaration(child)) {
      if (child.exportClause && child.moduleSpecifier) {
        const importName = child.moduleSpecifier.text;

        child.exportClause.forEachChild((node) => {
          if (ts.isExportSpecifier(node)) {
            exports[node.name.text] = {
              importPath: importName,
              isDefault: node.propertyName !== undefined,
            };
          }
        });
      }
    }
  });

  return exports;
};

/**
 * Given a result from the collectExports returns a
 * import module string for the given member
 */
const memberImportSolver = (libImportPath, mappings) => (member) => {
  const mapping = mappings[member];
  if (!mapping) {
    throw new Error(`Could not find mapping for ${member}`);
  }

  return path.join(libImportPath, mapping.importPath);
};

/**
 * Transforms the object from collectExports into a object
 * that has a key as the import name and the value as the alias original name
 */
const importAliases = (info) => {
  return Object.keys(info).reduce((aliases, key) => {
    const value = info[key];

    if (value.isDefault) {
      aliases[key] = 'default';
    } else {
      aliases[key] = key;
    }

    return aliases;
  }, {});
};

module.exports = {
  collectExports,
  memberImportSolver,
  importAliases,
};