Express HTTP Context 2
Modern request-scoped storage support for Express.js, based on native Node.js Asynchronous Local Storage. It's a great place to store user state, claims from a JWT, request/correlation IDs, and any other request-scoped data.
This package is a drop-in replacement and has been inspired by the work done in express-http-context, but with ESM support, no dependencies, and only supporting modern versions of Node.js (+v14).
Installation
npm install express-http-context2
yarn add express-http-context2
pnpm add express-http-context2
Requirements
express-http-context2
is a middleware intended for express
, so although it is not explicitly declared as a dependency or peer dependency, it requires express
to work, as well as @types/express
if you are using Typescript. The reason the dependency is not explicitly declared is that it could also eventually be used with fastify
or other Node.js HTTP servers.
Configuration
Use the middleware immediately before the first middleware that needs to have access to the context. You won't have access to the context in any middleware "used" before this one.
const express = require('express')
const httpContext = require('express-http-context2')
const app = express()
app.use(httpContext.middleware)
Note that some popular middlewares (such as body-parser
, express-jwt
) can cause the context to be lost. To work around such problems, it is recommended that you use any third-party middleware that does NOT require the context BEFORE using this middleware.
Usage
Examples of setting values:
const httpContext = require('express-http-context2')
const { nanoid } = require('nanoid')
app.use((req, res, next) => {
httpContext.set('userId', userId)
httpContext.set('requestId', nanoid())
})
Get them from anywhere in your code:
var httpContext = require('express-http-context2')
function logError(error) {
const userId = httpContext.get('userId')
const requestId = httpContext.get('requestId')
console.error(error, { userId, requestId })
}
API
middleware
It is an Express.js middleware that is responsible for initializing the independent context for each request. The get
and set
calls will operate on a set of keys/values unique to those contexts.
Example
import { middleware } from 'express-http-context2'
app.use(middleware)
set
Adds a value to the request context by key.
If the key already exists, its value will be overwritten.
No value will persist if the context has not yet been initialized.
Parameters
key
a string key to store the variable byvalue
any value to store under the key for the later lookup.
Example
import { set } from 'express-http-context2'
set('user', { id: 'overwrittenUser', email: 'foo@bar.com' })
get
Gets a value from the request context by key.
Will return undefined
if the context has not yet been initialized for this request or if a value is not found for the specified key.
Parameters
key
a string key to retrieve the stored value for
Example
import { get } from 'express-http-context2'
const user = get('user')
License
Express HTTP Context 2 is released under the MIT license:
MIT License
Copyright (c) 2023 Alberto Varela Sánchez
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.