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Middleware ​

You can add middleware to Workery applications.

A "middleware" is a function that works with every request before it is processed by any route handler function regardless of the state and content. And also with every response before returning it.

  • It takes each request that comes to your application.
  • It can then do something with that request or run any needed code.
  • Then it passes the request to be processed by route handlers.
  • It then takes the response returned by route handlers.
  • It can do something to that response or run any needed code.
  • Then it returns the response.

Declaration ​

To create a middleware you use the Middleware class to create a middleware instance.

The middleware init receives:

  • name: (optional) name of the middleware, this does not have any functional effect.
  • handle: the usual handler function, but with a second positional argument:
    • next: async function for calling the next handler in line, this could be the next middleware handler or the route handler itself. Returns a response.

Example:

ts
import { Middleware } from "workery"

const responseAddDate = new Middleware<Env>({
    handle: async ({}, next) => {
        const res = await next()
		res.headers.set("Date", new Date().toISOString())
		return res
    },
})

This example adds a Date header to all responses of the app. Remember to add the middleware to the app init for it to take effect.

ts
const app = new App<Env>({
	middleware: [
		responseAddDate,
	]
})

Middleware Order

The order of your middleware array is also the call order, the first middleware in the array is the first one to be called before route handlers and last one to be called after route handlers have returned a response.

Before & After Request ​

You can add code to be run before the request is processed by any route handler.

And also after the response is generated, before returning it.

ts
const myMiddleware = new Middleware<Env>({
    handle: async ({ req, env, ctx }, next) => {
        // code executed before route handlers
        const res = await next()
        // code executed after route handlers
		return res
    },
})

Runtime Gotchas

In Cloudflare Workers, Request (unpack arg req) objects are immutable, modifying this object results in error. Also, performance and timers only advance or increment after I/O occurs.

Built-in Middleware ​

Workery provides built-in middleware for common use-cases (even though they are not necessarily common in the context of Cloudflare Workers):