Azure Middleware Engine

1.0.1 verified Fri May 01 auth: no javascript

Azure Middleware Engine is a Node.js middleware engine for Azure Functions, inspired by Express, Fastify, and Hapi. Version 1.0.1 (stable) provides an intuitive API to apply middleware patterns in Azure Functions. It supports sequential middleware execution, conditional middleware via useIf, and validation. Alternatives like Azure Functions middleware libraries often lack chainable API or conditional execution. The package is lightweight with no external runtime dependencies, requiring Node >=8.9.4. It helps separate concerns like input parsing, validation, and error handling from business logic.

Common errors

error TypeError: MiddlewareHandler is not a constructor ↓

cause Importing the module incorrectly as default instead of named export.

fix

Use const { MiddlewareHandler } = require('azure-middleware');

error Error: next() called multiple times ↓

cause Calling next() more than once in a single middleware or after done().

fix

Ensure next() is called only once per middleware and not after context.done().

error Error: done already called ↓

cause Calling context.done() multiple times in the pipeline.

fix

Design pipeline so that only one middleware calls done() (typically the last).

Warnings

gotcha Missing next() call causes pipeline to hang. ↓

fix Always call context.next() in async or callback-style middlewares.

gotcha context.done() must be called exactly once; multiple calls may lead to race conditions. ↓

fix Ensure only one middleware calls context.done() and that it's called after all next() calls.

gotcha useIf predicate must return a boolean synchronously or via promise. ↓

fix Ensure predicate function returns a boolean or a promise resolving to boolean.

Install

npm install azure-middleware

yarn add azure-middleware

pnpm add azure-middleware

Imports

MiddlewareHandler

wrong

const MiddlewareHandler = require('azure-middleware');

correct

const { MiddlewareHandler } = require('azure-middleware');

Named export; common mistake to use default import.

MiddlewareHandler (ESM)

wrong

import MiddlewareHandler from 'azure-middleware';

correct

import { MiddlewareHandler } from 'azure-middleware';

ESM import available in Node versions supporting it.

azure-middleware (CommonJS entire module)
```
const azureMiddleware = require('azure-middleware');
```
Default export is an object with MiddlewareHandler property.

Quickstart

Shows basic middleware chain with context logging and response via context.done.

const { MiddlewareHandler } = require('azure-middleware');

const myFunction = new MiddlewareHandler()
  .use((context, next) => {
    context.log.info('First middleware');
    next();
  })
  .use((context, next) => {
    context.log.info('Second middleware');
    context.done(null, { body: 'Hello from Azure Function', status: 200 });
  })
  .listen();

module.exports = myFunction;