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Always FResh: Deno library for serving files, with optional client integration for CSS injection and page reload. Simpler, better alternative to tools like Browsersync and Livereload


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afr: Always Fresh. Tiny library for Deno. Simple and flexible file server, with optional "live reload" integration for development.

  • Serve from multiple directories.
  • Restrict paths via regexps or functions.
  • Optional: automatic .html or index.html fallbacks, just like GitHub Pages.
  • Optional: on file changes, reinject CSS or reload page.
  • Optional: partial Go implementation.


  • Collection of file-serving functions; see API.
  • Optional broadcaster:
    • Used inside your server, or via optional CLI.
    • Notifies clients.
    • Notification can be triggered by HTTP request from another process.
      • Allows page reload immediately after server restart. See examples.
  • Client component:
    • Tiny script.
    • Listens for server notifications.
    • Reinjects CSS without reloading. Reloads on other changes.

Other features:

  • Tiny and dependency-free. Being small is a big feature!
  • Doesn't force a separate server. Runs from within your Deno server, without complicating your environment. Optionally, run a broadcaster separately via CLI.
  • Can signal page reload after server restart. Extremely useful when developing a server-rendered app.
    • Implemented by running in a separate process, sending notifications from your main server process.
    • Accepts signals over HTTP, which can be sent from any process, from any language.

Super-lightweight alternative to other file-serving libraries, and also to tools like Browsersync, Livereload, etc.

This readme is for Deno. For Node support, see afr@0.3.2. For Go, see



As Library

For Deno (see API below):

import * as a from ''

For Go (see

import ""


The CLI doesn't serve files. It's a development tool that runs a broadcaster in a separate process, allowing clients to remain connected, so that your server can signal page reload on restart.

The following command runs the Deno CLI. This should be put in a makefile, and ran concurrently with your server. See examples. Requires Deno >= 1.13.0 or --unstable.

deno run --allow-net --allow-read --no-check --port 23456 --verbose true

Alternatively, use the equivalent Go CLI:

go install

afr --help

afr -v -p 23456


Runnable example: clone this repo, cd to examples, and run make.

Example server code has functionally-identical TS and JS versions (srv.ts and srv.mjs).


class Dir(path, filter)

ƒ(string|URL, RegExp|(string)=>bool)

Fundamental tool for serving files and handling FS events. Takes an FS path and an optional filter. For example:

const dir = a.dir('target', /[.](?:html|css|mjs)$/)

Many Afr functions require an array of dirs:

const dirs = [
  a.dir('.', /[.](?:html|css|mjs)$/),

The filter may be either a regexp or a function. Afr applies it to a path that is Posix-style (/-separated), relative to the dir, and not URL-encoded. Dirs without a filter are permissive and "allow" any sub-path when asked.

const dirs = [
  a.dir('.', /^(?:static|images|scripts)[/]/),

function resFile(req, dirs, opts)

ƒ(Request, []Dir, ResponseInit) -> Promise<Response | undefined>

Tries to serve a file specified by req.url from dirs.

dirs must be an array of Dir. They're used as mount points and filters. For each dir, req.url is resolved relative to that directory, and only the paths "allowed" by its filter may be served. Unlike most file-serving libraries, this allows you to easily and safely serve files out of .. In addition, this will automatically reject paths containing ...

Has limited content-type detection; see resExactFile for details.

File closing should be automatic; see resExactFile for details.

const dirs = [a.dir('target'), a.dir('.', /[.]html$/)]

async function response(req) {
  return (
    (await a.resFile(req, dirs)) ||
    new Response('not found', {status: 404})

function resSite(req, dirs, opts)

ƒ(Request, []Dir, ResponseInit) -> Promise<Response | undefined>

Same as resSiteWithNotFound, but without the 404.html fallback.

function resSiteWithNotFound(req, dirs, opts)

ƒ(Request, []Dir, ResponseInit) -> Promise<Response | undefined>

Variant of resFile that mimics GitHub Pages, Netlify, and other static-site hosting providers, by trying additional fallbacks when no exact match is found:

  • Try appending .html, unless the URL already looks like a file request or ends with /.
  • Try appending /index.html, unless the URL already looks like a file request.
  • Try serving 404.html with status code 404.

Extremely handy for developing a static site to be served by providers such as GitHub. Check examples for runnable examples.

const dirs = [a.dir('target'), a.dir('.', /[.]html$/)]

async function response(req) {
  return (
    (await a.resSiteWithNotFound(req, dirs)) ||
    new Response('not found', {status: 404})

function resExactFile(path, opts)

ƒ(string|URL, ResponseInit) -> Promise<Response>

Lower-level tool used by other file-serving functions. Serves a specific file, which must exist in the FS. path is anything accepted by; it may be a relative FS path, absolute FS path, or file URL.

Has limited content-type detection. If opts.headers doesn't already include content-type, tries to guess it by file extension. Known content types are stored in the contentTypes dictionary (exported but undocumented), which you can import and mutate.

Warning: this keeps the file open until the stream is fully read, or until res.body.cancel(). Both are handled automatically by Deno when serving the response, but it's your responsibility to immediately start serving this response. Otherwise the file descriptor may leak.

Warning: this may blindly serve any file from the filesystem. Never pass externally-provided paths such as req.url to this function. This must be used only for paths that are safe to publicly expose. For serving arbitrary files from a folder, use resFile or resSite.

async function response() {
  return (
    (await a.resExactFile('index.html')) ||
    (await a.resExactFile('404.html', {status: 404})) ||
    new Response('not found', {status: 404})

class Broad(opts)

interface BroadOpts {
  // URL pathname prefix for all Afr endpoints, including the client script.
  namespace?: string = '/afr/'

Short for "broadcaster". Handles Afr clients:

  • Serves client.mjs.
  • Maintains persistent connections from clients waiting for notifications.
  • Broadcasts notifications to those clients.
const bro = new a.Broad()

// Broadcasts a reload signal to all clients.
await bro.send({type: 'change'})

function serveFetchEvent(event) {
  return event.respondWith(response(event.request))

function response(req) {
  return bro.res(req) || new Response('fallback')

// Broadcasts a reload signal to all clients.
async function change() {
  await bro.send({type: 'change'})

Running Afr as a CLI starts an HTTP server that handles all requests using a Broad instance and responds with 404 to everything unknown.

Broad is also available in the Go port. See afr.go.

function send(msg, opts)

ƒ(any, SendOpts) -> Promise

interface SendOpts {
  url?: URL
  port?: number
  hostname?: string
  namespace?: string

Broadcasts msg to Afr clients. Assumes that on opts.url or opts.hostname + opts.port there is a reachable server that handles requests using Broad instance, and makes an HTTP request that causes that broadcaster to relay msg, as JSON, to every connected client.

This is useful when running Afr and your own server in separate processes. This allows clients to stay connected when your server restarts, and immediately reload when it's ready.

See the examples folder for a runnable example using this pattern.

const afrOpts = {port: 23456}
const dirs = [a.dir('target')]

// Call this when your server starts.
async function watch() {
  // May cause connected clients to immediately reload.
  a.maybeSend(a.change, afrOpts)

  // Watch files and notify clients about changes that don't involve restarting
  // the server, for example in CSS files.
  for await (const msg of'target', dirs, {recursive: true})) {
    await a.maybeSend(msg, afrOpts)

function maybeSend(msg, opts)

ƒ(any, SendOpts) -> Promise

Same as send, but ignores any connection errors.

function watch(path, dirs, opts)

ƒ(string|URL, []Dir, WatchOpts) -> AsyncIterator<FsEvent>

interface WatchOpts {
  recursive?: bool
  signal?: AbortSignal

interface FsEvent {
  type: string
  path: string

Wraps Deno.watchFs, converting FS events into messages understood by client.mjs.

path and opts are passed directly to the underlying FS watch API. dirs must be an array of Dir; they're used to convert absolute FS paths to relative URL paths, and to filter events via dir.allow.

To ignore certain paths, use dir filters; see Dir.

The resulting messages can be broadcast to connected clients via bro.send (when using a broadcaster in the same process) or send (when using an external process).

For cancelation, just break out of the loop or call .return() on the iterator. You can also pass opts.signal, which must be an AbortSignal, and later abort it.


const dirs = [a.dir('target'), a.dir('.', /[.]mjs$/)]

for await (const msg of'.', dirs, {recursive: true})) {
  await a.maybeSend(msg, afrOpts)


Some APIs are exported but undocumented to avoid bloating the docs. Check the source files and look for export.

Known Limitations

Supports only the built-in Deno HTTP server. For stdlib support, use afr@0.3.2.

No compression support. Put your Deno server behind a reverse proxy, such as Nginx, configured for compression.

No default HTTP cache headers. Caching strategies may vary. You should add your own cache headers. Afr makes it easy:

function respond(req) {return a.resFile(req, dirs, fileInit)}

const fileInit = {headers: {'cache-control': 'max-age=31536000'}}

For etag support, use slightly lower-level tools. Use the undocumented function resolveFile to get FS stats, generate an etag from that, then serve via resExactFile.



Revert v0.6.2.


Client stops auto-reconnecting after N attempts.


Add unlicense file for


Added a partial Go implementation. There are no changes in JS.


Minor TS tweak to satisfy some incorrect environmental lib definitions.


Now written in TS, courtesy of @pleshevskiy.


"File response" functions now return responses only for GET.


Corrected file extension parsing.


  • Support only Deno.
  • Support only built-in HTTP server.
  • Revamped many signatures to ƒ(Request) -> Response.


Improved the timing of the first response over a new HTTP connection when running via CLI in Node on Windows.


In Deno, when loading/running Afr by URL, Broad should now be able to serve the client script.


  • Support both Node and Deno.
  • Removed daemon features. Run Afr in foreground, in parallel with your server. Use Make to orchestrate build tasks and sub-processes.
  • Removed Watcher class; use watch to iterate over FS messages.
  • Removed Aio.
  • Removed Dirs.
  • Moved IO methods from Dirs and Dir into plain functions, with some minor renaming.


File server corrections for Windows compatibility (for real this time).


File server corrections for Windows compatibility.


Corrected minor race condition in CSS replacement.


Now an extra-powerful all-in-one.



I'm receptive to suggestions. If this library almost satisfies you but needs changes, open an issue or chat me up. Contacts:


Always FResh: Deno library for serving files, with optional client integration for CSS injection and page reload. Simpler, better alternative to tools like Browsersync and Livereload








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