grunt-contrib-watch
Advanced tools
Run predefined tasks whenever watched file patterns are added, changed or deleted
grunt-contrib-watch is a Grunt plugin that watches files and directories for changes. When changes are detected, it can run predefined tasks, making it useful for automating workflows such as compiling code, running tests, or refreshing a browser.
Watch Files for Changes
This feature allows you to watch JavaScript files for changes and run the 'jshint' task whenever a change is detected. The 'spawn' option is set to false to improve performance.
{
"watch": {
"scripts": {
"files": ["**/*.js"],
"tasks": ["jshint"],
"options": {
"spawn": false
}
}
}
}Live Reload
This feature enables live reloading of the browser when files change. The 'livereload' option is set to true, which will trigger a browser refresh whenever a watched file changes.
{
"watch": {
"options": {
"livereload": true
},
"scripts": {
"files": ["**/*.js"],
"tasks": ["jshint"]
}
}
}Custom Event Handling
This feature allows you to specify custom events to watch for, such as 'added' or 'deleted'. In this example, the 'jshint' task will run only when JavaScript files are added or deleted.
{
"watch": {
"scripts": {
"files": ["**/*.js"],
"tasks": ["jshint"],
"options": {
"event": ["added", "deleted"]
}
}
}
}gulp-watch is a Gulp plugin that provides file watching capabilities similar to grunt-contrib-watch. It allows you to watch files and directories for changes and run Gulp tasks in response. Compared to grunt-contrib-watch, gulp-watch is designed to work within the Gulp ecosystem, which is known for its simplicity and stream-based approach.
chokidar is a highly efficient and flexible file watcher library for Node.js. It provides a rich API for watching files and directories, and it can be used independently or integrated into other build tools. Compared to grunt-contrib-watch, chokidar offers more advanced features and better performance, making it suitable for large projects with complex file-watching needs.
nodemon is a utility that monitors for changes in your source and automatically restarts your Node.js application. While it is primarily used for restarting server applications, it can also be configured to watch for changes in other types of files. Compared to grunt-contrib-watch, nodemon is more focused on server-side development and provides automatic restarts rather than running arbitrary tasks.
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
Once the plugin has been installed, it may be enabled inside your Gruntfile with this line of JavaScript:
grunt.loadNpmTasks('grunt-contrib-watch');
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:
Type: String|Array
This defines what file patterns this task will watch. It can be a string or an array of files and/or minimatch patterns.
Type: String|Array
This defines which tasks to run when a watched file event occurs.
Type: Boolean
Default: true
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.
Example:
watch: {
scripts: {
files: ['**/*.js'],
tasks: ['jshint'],
options: {
spawn: false,
},
},
},
For backwards compatibility the option nospawn is still available and will do the opposite of spawn.
Type: Boolean
Default: false
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.
Example:
watch: {
scripts: {
files: '**/*.js',
tasks: ['jshint'],
options: {
interrupt: true,
},
},
},
Type: Integer
Default: 500
How long to wait before emitting events in succession for the same filepath and status. For example if your Gruntfile.js file was changed, a changed event will only fire again after the given milliseconds.
Example:
watch: {
scripts: {
files: '**/*.js',
tasks: ['jshint'],
options: {
debounceDelay: 250,
},
},
},
Type: Integer
Default: 100
The interval is passed to fs.watchFile. Since interval is only used by fs.watchFile and this watcher also uses fs.watch; it is recommended to ignore this option. Default is 100ms.
Type: String|Array
Default: 'all'
Specify the type of watch events that triggers the specified task. This option can be one or many of: 'all', 'changed', 'added' and 'deleted'.
Example:
watch: {
scripts: {
files: '**/*.js',
tasks: ['generateFileManifest'],
options: {
event: ['added', 'deleted'],
},
},
},
Type: Boolean
Default: false
By default, if Gruntfile.js is being watched, then changes to it will trigger the watch task to restart, and reload the Gruntfile.js changes.
When 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
}
}
}
Type: Boolean
Default: true
This is only a task level option and cannot be configured per target. By default the watch task will duck punch grunt.fatal and grunt.warn to try and prevent them from exiting the watch process. If you don't want grunt.fatal and grunt.warn to be overridden set the forever option to false.
Type: Function
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: {
dateFormat: function(time) {
grunt.log.writeln('The watch finished in ' + time + 'ms at' + (new Date()).toString());
grunt.log.writeln('Waiting for more changes...');
},
},
scripts: {
files: '**/*.js',
tasks: 'jshint',
},
},
Type: Boolean
Default: false
This option will trigger the run of each specified task at startup of the watcher.
Type: Boolean|Number|Object
Default: false
Set to true or set livereload: 1337 to a port number to enable live reloading. Default and recommended port is 35729.
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.
Example:
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 key and cert paths).
Example:
watch: {
css: {
files: '**/*.sass',
tasks: ['sass'],
options: {
livereload: {
host: 'localhost',
port: 9000,
key: grunt.file.read('path/to/ssl.key'),
cert: grunt.file.read('path/to/ssl.crt')
// you can pass in any other options you'd like to the https server, as listed here: http://nodejs.org/api/tls.html#tls_tls_createserver_options_secureconnectionlistener
}
},
},
},
Type: String|Object
Default: process.cwd()
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.
Type: Boolean
Default: true
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 deleted
grunt.initConfig({
watch: {
files: ['**/*'],
tasks: ['jshint'],
},
});
// Advanced config. Run specific tasks when specific files are added, changed or deleted.
grunt.initConfig({
watch: {
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'],
},
},
});
watch eventThis 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 watch event:
grunt.initConfig({
watch: {
scripts: {
files: ['lib/*.js'],
},
},
});
grunt.event.on('watch', function(action, filepath, target) {
grunt.log.writeln(target + ': ' + filepath + ' has ' + action);
});
The 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 jshint task:
grunt.initConfig({
watch: {
scripts: {
files: ['lib/*.js'],
tasks: ['jshint'],
options: {
spawn: false,
},
},
},
jshint: {
all: {
src: ['lib/*.js'],
},
},
});
// On watch events configure jshint:all to only run on changed file
grunt.event.on('watch', function(action, filepath) {
grunt.config('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 = Object.create(null);
var onChange = grunt.util._.debounce(function() {
grunt.config('jshint.all.src', Object.keys(changedFiles));
changedFiles = Object.create(null);
}, 200);
grunt.event.on('watch', function(action, filepath) {
changedFiles[filepath] = action;
onChange();
});
Live reloading is built into the watch task. Set the option livereload to true to enable on the default port 35729 or set to a custom port: livereload: 1337.
The simplest way to add live reloading to all your watch targets is by setting livereload to true at the task level. This will run a single live reload server and trigger the live reload for all your watch targets:
grunt.initConfig({
watch: {
options: {
livereload: true,
},
css: {
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:
grunt.initConfig({
watch: {
css: {
files: ['public/scss/*.scss'],
tasks: ['compass'],
options: {
// Start a live reload server on the default port 35729
livereload: true,
},
},
another: {
files: ['lib/*.js'],
tasks: ['anothertask'],
options: {
// Start another live reload server on port 1337
livereload: 1337,
},
},
dont: {
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 livereload.js script:
<script src="//localhost:35729/livereload.js"></script>
Feel free to add this script to your template situation and toggle with some sort of dev flag.
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 <script> tag.
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 instance
var lrserver = require('tiny-lr')();
// Listen on port 35729
lrserver.listen(35729, function(err) { console.log('LR Server Started'); });
// Then later trigger files or POST to localhost:35729/changed
lrserver.changed({body:{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 (sass, less, coffeescript, etc). As any file not recognized will reload the entire page as opposed to just the css or javascript.
The solution is to point a livereload watch target to your destination files:
grunt.initConfig({
sass: {
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 here
files: ['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 them
options: { livereload: true },
files: ['dest/**/*'],
},
},
});
EMFILE: Too many opened files.?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.
grunt-contrib-watch@0.1.x 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.
Another reason if you're watching a large number of files could be the low default interval. Try increasing with options: { interval: 5007 }. Please see issues #35 and #145 for more information.
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.
FAQs
Run predefined tasks whenever watched file patterns are added, changed or deleted
The npm package grunt-contrib-watch receives a total of 328,864 weekly downloads. As such, grunt-contrib-watch popularity was classified as popular.
We found that grunt-contrib-watch demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 6 open source maintainers collaborating on the project.
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