Run predefined tasks whenever watched file patterns are added, changed or deleted
Run predefined tasks whenever watched file patterns are added, changed or deleted
If you haven't used Grunt before, be sure to check out the Getting Started guide, as it explains how to create a Gruntfile as well as install and use Grunt plugins. Once you're familiar with that process, you may install this plugin with this command:
npm install grunt-contrib-watch --save-dev
Run this task with the
grunt watch command.
There are a number of options available. Please review the minimatch options here. As well as some additional options as follows:
This defines what file patterns this task will watch. It can be a string or an array of files and/or minimatch patterns.
This defines which tasks to run when a watched file event occurs.
Whether to spawn task runs in a child process. Setting this option to
false speeds up the reaction time of the watch (usually 500ms faster for most) and allows subsequent task runs to share the same context. Not spawning task runs can make the watch more prone to failing so please use as needed.
watch:scripts:files: '**/*.js'tasks: 'jshint'options:spawn: false
For backwards compatibility the option
nospawn is still available and will do the opposite of
As files are modified this watch task will spawn tasks in child processes. The default behavior will only spawn a new child process per target when the previous process has finished. Set the
interrupt option to true to terminate the previous process and spawn a new one upon later changes.
watch:scripts:files: '**/*.js'tasks: 'jshint'options:interrupt: true
How long to wait before emitting events in succession for the same filepath and status. For example if your
Gruntfile.js file was
changed event will only fire again after the given milliseconds.
watch:scripts:files: '**/*.js'tasks: 'jshint'options:debounceDelay: 250
interval is passed to
interval is only used by
fs.watchFile and this watcher also uses
fs.watch; it is recommended to ignore this option. Default is 100ms.
Specify the type of watch events that triggers the specified task. This option can be one or many of:
watch:scripts:files: '**/*.js'tasks: 'generateFileManifest'options:event: 'added' 'deleted'
By default, if
Gruntfile.js is being watched, then changes to it will trigger the watch task to restart, and reload the
reload is set to
true, changes to any of the watched files will trigger the watch task to restart.
This is especially useful if your
Gruntfile.js is dependent on other files.
watch:configFiles:files: 'Gruntfile.js' 'config/*.js'options:reload: true
This is only a task level option and cannot be configured per target. By default the watch task will duck punch
grunt.warn to try and prevent them from exiting the watch process. If you don't want
grunt.warn to be overridden set the
forever option to
This is only a task level option and cannot be configured per target. By default when the watch has finished running tasks it will display the message
Completed in 1.301s at Thu Jul 18 2013 14:58:21 GMT-0700 (PDT) - Waiting.... You can override this message by supplying your own function:
watch:options:grunt.logwriteln'The watch finished in ' + time + 'ms at' + toString;grunt.logwriteln'Waiting for more changes...';scripts:files: '**/*.js'tasks: 'jshint'
This option will trigger the run of each specified task at startup of the watcher.
true or set
livereload: 1337 to a port number to enable live reloading. Default and recommended port is
If enabled a live reload server will be started with the watch task per target. Then after the indicated tasks have run, the live reload server will be triggered with the modified files.
See also how to enable livereload on your HTML.
watch:css:files: '**/*.sass'tasks: 'sass'options:livereload: true
Passing an object to
livereload allows listening on a specific port and hostname/IP or over https connections (by specifying
watch:css:files: '**/*.sass'tasks: 'sass'options:livereload:host: 'localhost'port: 9000key: gruntfileread'path/to/ssl.key'cert: gruntfileread'path/to/ssl.crt'// you can pass in any other options you'd like to the https server, as listed here:
Ability to set the current working directory. Defaults to
process.cwd(). Can either be a string to set the cwd to match files and spawn tasks or an object to set each independently. Such as:
options:cwd:files: 'match/files/from/here'spawn: 'but/spawn/files/from/here'
To strip off a path before emitting events:
options:cwd:files: 'a/path'event: 'a/path'
This will strip off
a/path before emitting events. This option is useful for specifying the base directory to use with livereload.
Option to prevent the livereload if the executed tasks encountered an error. If set to
false, the livereload will only be triggered if all tasks completed successfully.
// Simple config to run jshint any time a file is added, changed or deletedgruntinitConfigwatch:files: '**/*'tasks: 'jshint';
// Advanced config. Run specific tasks when specific files are added, changed or deleted.gruntinitConfigwatch:gruntfile:files: 'Gruntfile.js'tasks: 'jshint:gruntfile'src:files: 'lib/*.js' 'css/**/*.scss' '!lib/dontwatch.js'tasks: 'default'test:files: '<%= jshint.test.src %>'tasks: 'jshint:test' 'qunit';
This task will emit a
watch event when watched files are modified. This is useful if you would like a simple notification when files are edited or if you're using this task in tandem with another task. Here is a simple example using the
gruntinitConfigwatch:scripts:files: 'lib/*.js';grunteventon'watch'grunt.logwritelntarget + ': ' + filepath + ' has ' + action;;
watch event is not intended for replacing the standard Grunt API for configuring and running tasks. If you're trying to run tasks from within the
watch event you're more than likely doing it wrong. Please read configuring tasks.
A very common request is to only compile files as needed. Here is an example that will only lint changed files with the
gruntinitConfigwatch:scripts:files: 'lib/*.js'tasks: 'jshint'options:spawn: falsejshint:all:src: 'lib/*.js';// On watch events configure jshint:all to only run on changed filegrunteventon'watch'gruntconfig'jshint.all.src' filepath;;
If you need to dynamically modify your config, the
spawn option must be disabled to keep the watch running under the same context.
If you save multiple files simultaneously you may opt for a more robust method:
var changedFiles = Objectcreatenull;var onChange = gruntutil_debouncegruntconfig'jshint.all.src' ObjectkeyschangedFiles;changedFiles = Objectcreatenull;200;grunteventon'watch'changedFilesfilepath = action;onChange;;
Live reloading is built into the watch task. Set the option
true to enable on the default port
35729 or set to a custom port:
The simplest way to add live reloading to all your watch targets is by setting
true at the task level. This will run a single live reload server and trigger the live reload for all your watch targets:
gruntinitConfigwatch:options:livereload: truecss:files: 'public/scss/*.scss'tasks: 'compass';
You can also configure live reload for individual watch targets or run multiple live reload servers. Just be sure if you're starting multiple servers they operate on different ports:
gruntinitConfigwatch:css:files: 'public/scss/*.scss'tasks: 'compass'options:// Start a live reload server on the default port 35729livereload: trueanother:files: 'lib/*.js'tasks: 'anothertask'options:// Start another live reload server on port 1337livereload: 1337dont:files: 'other/stuff/*'tasks: 'dostuff';
Once you've started a live reload server you'll be able to access the live reload script. To enable live reload on your page, add a script tag before your closing
</body> tag pointing to the
Feel free to add this script to your template situation and toggle with some sort of
Instead of adding a script tag to your page, you can live reload your page by installing a browser extension. Please visit how do I install and use the browser extensions for help installing an extension for your browser.
Once installed please use the default live reload port
35729 and the browser extension will automatically reload your page without needing the
Since live reloading is used when developing, you may want to disable building for production (and are not using the browser extension). One method is to use Connect middleware to inject the script tag into your page. Try the connect-livereload middleware for injecting the live reload script into your page.
Live reloading is made easy by the library tiny-lr. It is encouraged to read the documentation for
tiny-lr. If you would like to trigger the live reload server yourself, simply POST files to the URL:
http://localhost:35729/changed. Or if you rather roll your own live reload implementation use the following example:
// Create a live reload server instancevar lrserver = require'tiny-lr';// Listen on port 35729lrserverlisten35729 console.log'LR Server Started'; ;// Then later trigger files or POST to localhost:35729/changedlrserverchangedbody:files:'public/css/changed.css';
Any time a watched file is edited with the
livereload option enabled, the file will be sent to the live reload server. Some edited files you may desire to have sent to the live reload server, such as when preprocessing (
coffeescript, etc). As any file not recognized will reload the entire page as opposed to just the
The solution is to point a
livereload watch target to your destination files:
gruntinitConfigsass:dev:src: 'src/sass/*.sass'dest: 'dest/css/index.css'watch:sass:// We watch and compile sass files as normal but don't live reload herefiles: 'src/sass/*.sass'tasks: 'sass'livereload:// Here we watch the files the sass task will compile to// These files are sent to the live reload server after sass compiles to themoptions: livereload: truefiles: 'dest/**/*';
This is because of your system's max opened file limit. For OSX the default is very low (256). Temporarily increase your limit with
ulimit -n 10480, the number being the new max limit.
In some versions of OSX the above solution doesn't work. In that case try
launchctl limit maxfiles 10480 10480 and restart your terminal. See here.
email@example.com is compatible with Grunt v0.3 but it is highly recommended to upgrade Grunt instead.
Likely because of an enthusiastic pattern trying to watch thousands of files. Such as
'**/*.js' but forgetting to exclude the
node_modules folder with
'!**/node_modules/**'. Try grouping your files within a subfolder or be more explicit with your file matching pattern.
The goal of this watch task is as files are changed, run tasks as if they were triggered by the user himself or herself. Each time a user runs
grunt a process is spawned and tasks are ran in succession. In an effort to keep the experience consistent and continually produce expected results, this watch task spawns tasks as child processes by default.
Sandboxing task runs also allows this watch task to run more stable over long periods of time. As well as more efficiently with more complex tasks and file structures.
Spawning does cause a performance hit (usually 500ms for most environments). It also cripples tasks that rely on the watch task to share the context with each subsequent run (i.e., reload tasks). If you would like a faster watch task or need to share the context please set the
spawn option to
false. Just be aware that with this option enabled, the watch task is more prone to failure.
Instead of restarting your server each time a static file is changed, start a static web server using (grunt-contrib-connect)[https://github.com/gruntjs/grunt-contrib-connect].
You'll have the
connect web server on seperate port ex: port 9000 from your main server. When the 'livereload' option is enabled for 'watch' tasks, it will handle triggerring the live reload server for each tasks and when files are modified, which then server back to main server ex: 3000. The main server must include a script tag or a browser extension to the livereload server in order for the browser automatically.
Task submitted by Kyle Robinson Young
This file was generated on Sat Mar 12 2016 14:08:17.