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watch mode for browserify builds

build status

Update any source file and your browserify bundle will be recompiled on the spot.


$ watchify main.js -o static/bundle.js

Now as you update files, static/bundle.js will be automatically incrementally rebuilt on the fly.

The -o option can be a file or a shell command (not available on Windows) that receives piped input:

watchify main.js -o 'exorcist static/ > static/bundle.js' -d
watchify main.js -o 'uglifyjs -cm > static/bundle.min.js'

You can use -v to get more verbose output to show when a file was written and how long the bundling took (in seconds):

$ watchify browser.js -d -o static/bundle.js -v
610598 bytes written to static/bundle.js (0.23 seconds) at 8:31:25 PM
610606 bytes written to static/bundle.js (0.10 seconds) at 8:45:59 PM
610597 bytes written to static/bundle.js (0.14 seconds) at 8:46:02 PM
610606 bytes written to static/bundle.js (0.08 seconds) at 8:50:13 PM
610597 bytes written to static/bundle.js (0.08 seconds) at 8:58:16 PM
610597 bytes written to static/bundle.js (0.19 seconds) at 9:10:45 PM


Use watchify with all the same options as browserify except that -o (or --outfile) is mandatory. Additionally, there are also:

Standard Options:
  --outfile=FILE, -o FILE
    This option is required. Write the browserify bundle to this file. If
    the file contains the operators `|` or `>`, it will be treated as a
    shell command, and the output will be piped to it.
  --verbose, -v                     [default: false]
    Show when a file was written and how long the bundling took (in
    Show the watchify and browserify versions with their module paths.
Advanced Options:
  --delay                           [default: 100]
    Amount of time in milliseconds to wait before emitting an "update"
    event after a change.
  --ignore-watch=GLOB, --iw GLOB    [default: false]
    Ignore monitoring files for changes that match the pattern. Omitting
    the pattern will default to "**/node_modules/**".
  --poll=INTERVAL                   [default: false]
    Use polling to monitor for changes. Omitting the interval will default
    to 100ms. This option is useful if you're watching an NFS volume.


var watchify = require('watchify');

watchify(b, opts)

watchify is a browserify plugin, so it can be applied like any other plugin. However, when creating the browserify instance b, you MUST set the cache and packageCache properties:

var b = browserify({ cache: {}, packageCache: {} });
var b = browserify({
  cache: {},
  packageCache: {},
  plugin: [watchify]

By default, watchify doesn't display any output, see events for more info.

b continues to behave like a browserify instance except that it caches file contents and emits an 'update' event when a file changes. You should call b.bundle() after the 'update' event fires to generate a new bundle. Calling b.bundle() extra times past the first time will be much faster due to caching.

Important: Watchify will not emit 'update' events until you've called w.bundle() once and completely drained the stream it returns.

var fs = require('fs');
var browserify = require('browserify');
var watchify = require('watchify');
var b = browserify({
  entries: ['path/to/entry.js'],
  cache: {},
  packageCache: {},
  plugin: [watchify]
b.on('update', bundle);
function bundle() {


You can to pass an additional options object as a second parameter of watchify. Its properties are:

opts.delay is the amount of time in milliseconds to wait before emitting an "update" event after a change. Defaults to 100.

opts.ignoreWatch ignores monitoring files for changes. If set to true, then **/node_modules/** will be ignored. For other possible values see Chokidar's documentation on "ignored".

opts.poll enables polling to monitor for changes. If set to true, then a polling interval of 100ms is used. If set to a number, then that amount of milliseconds will be the polling interval. For more info see Chokidar's documentation on "usePolling" and "interval". This option is useful if you're watching an NFS volume.

var b = browserify({ cache: {}, packageCache: {} });
// watchify defaults: 
b.plugin(bundle, {
  delay: 100,
  ignoreWatch: ['**/node_modules/**'],
  poll: false


Close all the open watch handles.


b.on('update', function (ids) {})

When the bundle changes, emit the array of bundle ids that changed.

b.on('bytes', function (bytes) {})

When a bundle is generated, this event fires with the number of bytes.

b.on('time', function (time) {})

When a bundle is generated, this event fires with the time it took to create the bundle in milliseconds.

b.on('log', function (msg) {})

This event fires after a bundle was created with messages of the form:

X bytes written (Y seconds)

with the number of bytes in the bundle X and the time in seconds Y.


With npm do:

$ npm install -g watchify

to get the watchify command and:

$ npm install watchify

to get just the library.


rebuilds on OS X never trigger

It may be related to a bug in fsevents (see #250 and stackoverflow). Try the --poll flag and/or renaming the project's directory - that might help.

see also

  • budo – a simple development server built on watchify
  • errorify – a plugin to add error handling to watchify development
  • watchify-request – wraps a watchify instance to avoid stale bundles in HTTP requests
  • watchify-middleware – similar to watchify-request, but includes some higher-level features