babel/packages/babel-plugin-transform-jscript/src/index.js

export default function ({ types: t }) {
  return {
    visitor: {
      FunctionExpression: {
        exit(path) {
          let { node } = path;
          if (!node.id) return;
          node._ignoreUserWhitespace = true;

          path.replaceWith(t.callExpression(
            t.functionExpression(null, [], t.blockStatement([
              t.toStatement(node),
              t.returnStatement(node.id)
            ])),
            []
          ));
        }
      }
    }
  };
}