1.9.1 • Public • Published



A simple middleware for watchify which provides a few features for a better development experience:

  • suspends the server response so you are never served a stale or empty bundle
  • removes the default 600ms delay (left up to the developer to reconfigure)
  • emits timing information in a 'log' event
  • (optional) allows for a browser-based error handler (eg: print to DevTools console)

For practical implementations, see watchify-server or budo.


npm install watchify-middleware --save


var watchifyMiddleware = require('watchify-middleware')
var defaultIndex = require('simple-html-index')

var staticUrl = 'bundle.js'
var bundler = browserify('app.js', {
  // config for watchify
  cache: {}, 
  packageCache: {},
  basedir: __dirname 
var watchify = watchifyMiddleware(bundler)

var server = http.createServer(function (req, res) {
  if (req.url === '/') {
    defaultIndex({ entry: staticUrl }).pipe(res)
  } else if (req.url === '/' + staticUrl) {
    watchify(req, res)

server.listen(8000, 'localhost', function () {
  console.log('Listening on http://localhost:8000/')

For a more complete example, see example/server.js.



middleware = watchifyMiddleware(browserify[, opt])

Returns a middleware(req, res) function from the given browserify bundler instance and options:

  • delay (default 0) a delay to debounce the rebuild, useful for things like git branch switches (where hundreds of files may change at once)
  • errorHandler (default false) a boolean or function for handling errors
  • initialBundle (default true) whether to initially bundle and emit 'pending'

errorHandler can be a function that accepts (err) parameter and optionally returns the new contents (String|Buffer) of the JavaScript bundle. If errorHandler is true, it will default to the following:

var stripAnsi = require('strip-ansi')

function defaultErrorHandler (err) {
  console.error('%s', err)
  var msg = stripAnsi(err.message)
  return ';console.error(' + JSON.stringify(msg) + ');'

(some plugins produce ANSI color codes in error messages)

Otherwise, it assumes the normal behaviour for error handling (which is typically just an uncaught error event).

emitter = watchifyMiddleware.emitter(browserify[, opt])

The same as above, except this returns an EventEmitter for handling bundle updates.


The middleware(req, res) function for use in your server.


Triggers a bundle event. Usually should only be called if initialBundle is set to false, to trigger the initial bundle.

emitter.on('pending', fn)

Called when watchify begins its incremental rebuild.

emitter.on('update', fn)

Called when bundling is finished, with parameter (contents, rows).

contents is a Buffer/String of the bundle and rows is a list of dependencies that have changed since last update. On first run, this will be an empty array.

emitter.on('log', fn)

Provides timing and server request logging, passing an (event) parameter.

Server request logs look like this:

{ level: 'debug', type: 'request', message: 'bundle (pending|ready)'}

Bundle updates look like this:

{ elapsed: Number, level: 'info', type: 'bundle' }

These events work well with garnish and other ndjson-based tools.

emitter.on('error', fn)

If errorHandler was fasle, this will get triggered on bundle errors. If an error handler is being used, this will not get triggered.

emitter.on('bundle-error', fn)

This will get triggered on bundle errors, regardless of whether errorHandler is being used. This can be used to respond to syntax errors, such as showing a stylized notification.


Closes the watchify instance and stops file watching.

version = watchifyMiddleware.getWatchifyVersion()

Primarily useful for debugging, this will return the actual version number of the watchify module being used by watchify-middleware.

running the demo

To run the example, first git clone and install dependencies.

git clone
cd watchify-middleware
npm install


npm start

And open http://localhost:8000/. Try making changes to example/app.js and you will see timing information in console, and reloading the browser will provide the new bundle.


MIT, see for details.

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npm i watchify-middleware

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