TypeScript and export HelmetOptions

Hi,

We have a function that looks similar to:

/**
 * Get a list of default Helmet options we use for e.g. our
 * http and websocket (socket.io) routes.
 *
 * @returns {HelmetOptions} The options to use with Helmet
 */
function getHelmetOptions() {
  return {
    hsts: {
      maxAge: 31536000,
    },
    expectCt: false,
  };
}

The reason is we use these options both for basic Express apps but also for socket.io routes. But there is no way to import the HelmetOptions interface like import {HelmetOptions} from "helmet";

Could you, in addition to the default export, also export the named export HelmetOptions for usage scenarios like above?

[EvanHahn]

I think only attempt 3 should succeed, so things are working as expected. (I think!)

Attempt 1 is trying to import HelmetOptions which is a TypeScript type. You can’t import TypeScript types from plain JavaScript, so this shouldn’t work.

Attempt 2 imports Helmet’s default export, not the Helmet namespace. HelmetOptions is not part of the default export, so this shouldn’t work either. It seems that Express works differently.

Attempt 3 imports Helmet as a namespace. HelmetOptions is part of that namespace, so it should work.

Hope this helps.

[thernstig]

@EvanHahn I tested a few things with this and have some findings. My knowledge of TypeScript is not good enough to deduct if there is something that can be done or not, but wanted to share. Note we are not using TypeScript directly in our code, but more the TypeScript in JSDoc (via a jsconfig.json) which is how some editors support TypeScript in JavaScript projects, such as VS Code.

Attempt 1 (failed)

import { HelmetOptions } from 'helmet';

/**
 * Get a list of default Helmet options
 *
 * @returns {HelmetOptions} The options to use with Helmet
 */

# This fails during running node with the above code
file:///home/userA/code/projectA/server/util/security.js:1
import { HelmetOptions } from 'helmet';
         ^^^^^^^^^^^^^
SyntaxError: The requested module 'helmet' does not provide an export named 'HelmetOptions'
    at ModuleJob._instantiate (node:internal/modules/esm/module_job:124:21)
    at async ModuleJob.run (node:internal/modules/esm/module_job:181:5)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:281:24)
    at async loadESM (node:internal/process/esm_loader:88:5)
    at async handleMainPromise (node:internal/modules/run_main:65:12)

Attempt 2 (failed)

import helmet from 'helmet';

/**
 * Get a list of default Helmet options
 *
 * @returns {helmet.HelmetOptions} The options to use with Helmet
 */

Attempt 3 (passed)

import * as helmet from 'helmet';

/**
 * Get a list of default Helmet options
 *
 * @returns {helmet.HelmetOptions} The options to use with Helmet
 */

Alternate example with the express module (passes)

import express from 'express';

/**
 * Some function
 *
 * @returns {express.Request} Express req object
 */

As you can see for some reason at least the Express example works, which mimics attempt 2.