babel/packages/babel-helper-split-export-declaration/src/index.ts

import {
  cloneNode,
  exportNamedDeclaration,
  exportSpecifier,
  identifier,
  variableDeclaration,
  variableDeclarator,
} from "@babel/types";

export default function splitExportDeclaration(exportDeclaration) {
  if (!exportDeclaration.isExportDeclaration()) {
    throw new Error("Only export declarations can be split.");
  }

  // build specifiers that point back to this export declaration
  const isDefault = exportDeclaration.isExportDefaultDeclaration();
  const declaration = exportDeclaration.get("declaration");
  const isClassDeclaration = declaration.isClassDeclaration();

  if (isDefault) {
    const standaloneDeclaration =
      declaration.isFunctionDeclaration() || isClassDeclaration;

    const scope = declaration.isScope()
      ? declaration.scope.parent
      : declaration.scope;

    let id = declaration.node.id;
    let needBindingRegistration = false;

    if (!id) {
      needBindingRegistration = true;

      id = scope.generateUidIdentifier("default");

      if (
        standaloneDeclaration ||
        declaration.isFunctionExpression() ||
        declaration.isClassExpression()
      ) {
        declaration.node.id = cloneNode(id);
      }
    }

    const updatedDeclaration = standaloneDeclaration
      ? declaration
      : variableDeclaration("var", [
          variableDeclarator(cloneNode(id), declaration.node),
        ]);

    const updatedExportDeclaration = exportNamedDeclaration(null, [
      exportSpecifier(cloneNode(id), identifier("default")),
    ]);

    exportDeclaration.insertAfter(updatedExportDeclaration);
    exportDeclaration.replaceWith(updatedDeclaration);

    if (needBindingRegistration) {
      scope.registerDeclaration(exportDeclaration);
    }

    return exportDeclaration;
  }

  if (exportDeclaration.get("specifiers").length > 0) {
    throw new Error("It doesn't make sense to split exported specifiers.");
  }

  const bindingIdentifiers = declaration.getOuterBindingIdentifiers();

  const specifiers = Object.keys(bindingIdentifiers).map(name => {
    return exportSpecifier(identifier(name), identifier(name));
  });

  const aliasDeclar = exportNamedDeclaration(null, specifiers);

  exportDeclaration.insertAfter(aliasDeclar);
  exportDeclaration.replaceWith(declaration.node);
  return exportDeclaration;
}