Context Storage Middleware

The Context Storage Middleware stores the Hono Context in the AsyncLocalStorage, to make it globally accessible.

INFO

Note This middleware uses AsyncLocalStorage. The runtime should support it.

Cloudflare Workers: To enable AsyncLocalStorage, add the nodejs_compat or nodejs_als flag to your wrangler.toml file.

Import

import { Hono } from 'hono'
import {
  contextStorage,
  getContext,
  tryGetContext,
} from 'hono/context-storage'

Usage

The getContext() will return the current Context object if the contextStorage() is applied as a middleware.

type Env = {
  Variables: {
    message: string
  }
}

const app = new Hono<Env>()

app.use(contextStorage())

app.use(async (c, next) => {
  c.set('message', 'Hello!')
  await next()
})

// You can access the variable outside the handler.
const getMessage = () => {
  return getContext<Env>().var.message
}

app.get('/', (c) => {
  return c.text(getMessage())
})

On Cloudflare Workers, you can access the bindings outside the handler.

type Env = {
  Bindings: {
    KV: KVNamespace
  }
}

const app = new Hono<Env>()

app.use(contextStorage())

const setKV = (value: string) => {
  return getContext<Env>().env.KV.put('key', value)
}

tryGetContext

tryGetContext() works like getContext(), but returns undefined instead of throwing an error when the context is not available:

const context = tryGetContext<Env>()
if (context) {
  // Context is available
  console.log(context.var.message)
}