Polkadot Middleware

1.0.1 · active · verified Wed Apr 22

The `polkadot-middleware` package provides a familiar middleware pattern for the `polkadot` HTTP server, streamlining request handler composition. Currently at version 1.0.1, it offers a functional alternative to manual function nesting, simplifying the development of server-side logic. This library addresses the current lack of a native pipeline operator in JavaScript, allowing developers to chain asynchronous request/response functions linearly. It serves a specific niche for users of the lightweight `polkadot` server who desire an Express.js-like middleware experience without significant overhead, focusing on readability and maintainability for simple API servers.

Common errors

```
TypeError: polkadot is not a function
```
cause The `polkadot` package was not installed or incorrectly imported, or an older version of `polkadot` with a different API is being used.

fix Run `npm install polkadot` or `yarn add polkadot`. Verify your `polkadot` import statement matches its export type (e.g., `import polkadot from 'polkadot'` for ESM).
```
ReferenceError: middleware is not defined
```
cause The `polkadot-middleware` package was not installed, incorrectly imported, or the import path is wrong.

fix Run `npm install polkadot-middleware` or `yarn add polkadot-middleware`. Ensure the import statement is correct, typically `import middleware from 'polkadot-middleware'` or `const middleware = require('polkadot-middleware')`.

Warnings

gotcha The primary utility of `polkadot-middleware` is as a temporary solution until the TC39 pipeline operator proposal is fully adopted and implemented in JavaScript runtimes. Once standardized, native language features may offer a more direct and potentially performant way to achieve similar composition.
Fix: No immediate fix required, but be aware of future language changes that might make this library less critical.
gotcha This library is specifically designed for the `polkadot` HTTP server. It is not a general-purpose middleware solution and cannot be directly applied to other Node.js HTTP frameworks like Express.js, Koa, or Fastify.
Fix: Ensure you are using `polkadot` as your HTTP server. For other frameworks, use their native middleware solutions.

Install

npm install polkadot-middleware npm
yarn add polkadot-middleware yarn
pnpm add polkadot-middleware pnpm

Imports

middleware

wrong:

const { middleware } = require('polkadot-middleware')

correct:

import middleware from 'polkadot-middleware'

The library primarily uses a default export pattern for both CJS and ESM.

polkadot
wrong:
```
const { polkadot } = require('polkadot')
```
correct:
```
import polkadot from 'polkadot'
```
`polkadot` itself is typically imported as a default export.

Quickstart

Demonstrates chaining multiple middleware functions for error handling and cache control with a basic response using `polkadot-middleware`.

import polkadot from 'polkadot';
import middleware from 'polkadot-middleware';

async function handleErrors(next) {
	return async (req, res) => {
		try {
			return await next(req, res);
		} catch (err) {
			res.statusCode = 500;
			return err.message || err;
		}
	};
}

async function setCacheControl(next) {
	return async (req, res) => {
		res.setHeader(`Cache-Control`, `public, max-age=` + 3600);
		return next(req, res);
	};
}

middleware(
	polkadot,
	handleErrors,
	setCacheControl,
	(req, res) => 'Sup dawg'
).listen(8080, () => console.log('Server listening on http://localhost:8080'));

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