express-http-context

What is express-http-context?

The express-http-context package provides a way to manage and access context data across the lifecycle of an HTTP request in an Express application. This is particularly useful for scenarios where you need to share data between middleware and route handlers without explicitly passing it around.

What are express-http-context's main functionalities?

Set and Get Context Data

This feature allows you to set and get context data within the lifecycle of an HTTP request. In this example, user data is set in the context in a middleware and then accessed in a route handler.

const express = require('express');
const httpContext = require('express-http-context');

const app = express();
app.use(httpContext.middleware);

app.use((req, res, next) => {
  httpContext.set('user', { id: 1, name: 'John Doe' });
  next();
});

app.get('/', (req, res) => {
  const user = httpContext.get('user');
  res.send(`Hello, ${user.name}`);
});

app.listen(3000, () => console.log('Server running on port 3000'));

Namespace Isolation

This feature ensures that context data is isolated per request by binding the request and response objects to the context namespace. This is useful for tracking request-specific data like request IDs.

const express = require('express');
const httpContext = require('express-http-context');

const app = express();
app.use(httpContext.middleware);

app.use((req, res, next) => {
  httpContext.ns.bindEmitter(req);
  httpContext.ns.bindEmitter(res);
  next();
});

app.use((req, res, next) => {
  httpContext.set('requestId', req.headers['x-request-id']);
  next();
});

app.get('/', (req, res) => {
  const requestId = httpContext.get('requestId');
  res.send(`Request ID: ${requestId}`);
});

app.listen(3000, () => console.log('Server running on port 3000'));

Other packages similar to express-http-context

cls-hooked

cls-hooked is a continuation-local storage package that provides a way to maintain context across asynchronous operations. It is more general-purpose compared to express-http-context and can be used outside of Express applications. However, it requires more setup to integrate with Express.

async-local-storage

async-local-storage is a built-in Node.js module that provides an API for maintaining context across asynchronous operations. It is similar to cls-hooked but is part of the Node.js core. It offers a more standardized approach but may require additional boilerplate to use effectively with Express.

README

Express HTTP Context

Get and set request-scoped context anywhere. This package is an unopinionated, zero-dependency, Express-idiomatic implementation of Node AsyncLocalStorage. It's a great place to store user state, claims from a JWT, request/correlation IDs, and any other request-scoped data.

How to use it

Install: npm i express-http-context

Use the context middleware before the first middleware or handler that needs to have access to the context.

import express from 'express';
import * as httpContext from 'express-http-context';

const app = express();
app.use(httpContext.middleware);
// All code from here on has access to the same context for each request

Set values based on the incoming request:

// Example authentication middleware
app.use(async (req, res, next) => {
	try {
		// Get user from data on request
		const bearer = req.get('Authorization');
		const user = await userService.getUser(bearer);

		// Add user to the request-scoped context
		httpContext.set('user', user);

		return next();
	} catch (err) {
		return next(err);
	}
});

Get them from code that doesn't have access to the express req object:

import * as httpContext from 'express-http-context';

// Somewhere deep in the Todo Service
async function createTodoItem(title, content) {
	// Get the user from the request-scoped context
	const user = httpContext.get('user');

	await db.insert({ title, content, userId: user.id });
}

Legacy versions

• For Node <7: npm install --save express-http-context@0
• For Node >=8 <12: npm install --save express-http-context@1

Contributors

• Steve Konves (@skonves)
• Amiram Korach (@amiram)
• Yoni Rabinovitch (@yonirab)
• DontRelaX (@dontrelax)
• William Durand (@willdurand)
• Kristopher Morris (@beeduck)

Interesting in contributing? Take a look at the Contributing Guidlines