Reload your babel-node app on JS source file changes. And do it *fast*.

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7.8.15 months ago8 years agoMinified + gzip package size for babel-watch in KB


Reload your babel-node app on JS source file changes. And do it fast.

Why should I use it?

If you're tired of using babel-node together with nodemon, babel/cli with --watch option (or similar solution). The reason why the aforementioned setup performs so badly is the startup time of babel-node itself. babel-watch only starts babel in the "master" process where it also starts the file watcher. The transpilation is performed in that process too. On file-watcher events, it spawns a pure node process and passes transpiled code from the parent process together with the source maps. This allows us to avoid loading babel and all its deps every time we restart the JS script/app.


A unique feature of babel-watch is capability of automatically detecting files that needs to be watched. You no longer need to specify the list of files or directories to watch for. With "autowatch" the only thing you need to do is to pass the name of your main script and babel-watch will start watching for the changes on files that are loaded by your node program while it is executing. (You can disable autowatch with -D option or exclude some directories from being watched automatically with -x).

System requirements

Currently babel-watch is supported on Linux, OSX and Windows.

I want it

Just install it and add to your package:
With NPM:
npm install --save-dev babel-watch

With Yarn:
yarn add --dev babel-watch

(Make sure you have @babel/core installed as dependency in your project as babel-watch only defines @babel/core as a "peerDependency")
Then use babel-watch in your package.json in scripts section like this:
"scripts": {
  "start": "babel-watch src/main.js"


babel-watch was made to be compatible with babel-node and nodemon options. Not all of them are supported yet, here is a short list of supported command line options:
-d, --debug [port]             Enable debug mode (deprecated) with optional port
-B, --debug-brk                Enable debug break mode (deprecated)
-I, --inspect [address]        Enable inspect mode
-X, --inspect-brk [address]    Enable inspect break mode
-o, --only [globs]             Matching files will *only* be transpiled (default: null)
-i, --ignore [globs]           Matching files will not be transpiled, but will still be watched. Default value is "node_modules". If you specify this option and still want to exclude modules, be sure to add it to the list. (default: ["node_modules"])
-e, --extensions [extensions]  List of extensions to hook into (default: [".js",".jsx",".es6",".es",".mjs"])
-w, --watch [dir]              Watch directory "dir" or files. Use once for each directory or file to watch (default: [])
-x, --exclude [dir]            Exclude matching directory/files from watcher. Use once for each directory or file (default: [])
-L, --use-polling              In some filesystems watch events may not work correcly. This option enables "polling" which should mitigate this type of issue
-D, --disable-autowatch        Don't automatically start watching changes in files "required" by the program
-H, --disable-ex-handler       Disable source-map-enhanced uncaught exception handler. You may want to use this option in case your app registers a custom uncaught exception handler
-m, --message [string]         Set custom message displayed on restart (default: ">>> Restarting due to change in file(s): %s")
-c, --config-file [string]     Babel config file path
--clear-console                If set, will clear console on each restart. Restart message will not be shown
--before-restart <command>     Set a custom command to be run before each restart, for example "npm run lint"
--restart-timeout <ms>         Set the maximum time to wait before forcing a restart. Useful if your app does graceful cleanup. (default: 2000)
--no-colors                    Don't use console colors
--restart-command <command>    Set a string to issue a manual restart. Set to `false` to pass stdin directly to process. (default: "rs")
--no-debug-source-maps         When using "--inspect" options, inline source-maps are automatically turned on. Set this option to disable that behavior
-V, --version                  output the version number
-h, --help                     display help for command

While the babel-watch process is running you may type "rs" and hit return in the terminal to force reload the app.

Node Options

To pass options directly to the Node child that are not shown above, use BABEL_WATCH_NODE_OPTIONS. For example:
BABEL_WATCH_NODE_OPTIONS="--experimental-worker" babel-watch app.js

Note not to use NODE_OPTIONS. This will apply the options to both the file watcher and the child process, which may have undesired effects with certain options like --inspect.

Example usage:

In most of the cases you would rely on "autowatch" to monitor all the files that are required by your node application. In that case you just run:
babel-watch app.js

If you have your view templates (build with pug, mustache or any other templating library) in the directory called views, autowatch will not be able to detect changes in view template files (see why) , so you need to pass in that directory name using --watch option:
babel-watch --watch views app.js

When you want your app not to restart automatically for some set of files, you can use --exclude option:
babel-watch --exclude templates app.js

Start the debugger
babel-watch app.js --debug 5858


Demo of nodemon + babel-node (on the left) and babel-watch reloading simple express based app:

Do not use in production

Using babel-node or babel-watch is not recommended in production environment. For the production use it is much better practice to build your node application using babel and run it using just node.

Babel compatibility

babel-watch's versions now mirror the major version range of the Babel version it is compatible with. Currently, that is 7.x.
  • babel-watch >= 2.0.7 (and now 7.x) is compatible with @babel/core version 7.0.0 and above
  • babel-watch < 2.0.7 && >= 2.0.2 is compatible with babel-core version 6.5.1
  • babel-watch <= 2.0.1 is compatible with babel-core from 6.4.x up to 6.5.0

(This is due to the babel's "option manager" API change in babel-core@6.5.1)

What's the difference between --ignore and --exclude?

These options seem very similar, and so there is some confusion about them. The difference is:
  • --ignore will watch the file, but not transpile it with Babel.
- Use if you have JS files in your project that are not transpiled or handled by some other tool, but you still want to restart when they change. - This is called --ignore to mirror the Babel option.
  • --exclude will not watch the file at all and thus it won't be transpiled either.
- Use if you want the watcher to exclude these files entirely. They will not be watched or rebuilt at all. For many projects, judicious use of --exclude can really speed things up.



If you want to know which file caused a restart, or why a file was not processed, add env DEBUG="babel-watch:*" before your command to see babel-watch internals. Please do this before filing a bug report.

Application doesn't restart automatically

There are a couple of reasons that could be causing that:
  1. You filesystem configuration doesn't trigger filewatch notification (this could happen for example when you have babel-watch running within docker container and have filesystem mirrored). In that case try running babel-watch with -L option which will enable polling for file changes.
  2. Files you're updating are blacklisted. Check the options you pass to babel-watch and verify that files you're updating are being used by your app and their name does not fall into any exclude pattern (option -x or --exclude).

Application doesn't restart when I change one of the view templates (html file or similar):

You perhaps are using autowatch. Apparently since view templates are not loaded using require command but with instead, therefore autowatch is not able to detect that they are being used. You can still use autowatch for all the js sources, but need to specify the directory name where you keep your view templates so that changes in these files can trigger app restart. This can be done using --watch option (e.g. babel-watch --watch views app.js).

I'm getting an error: Cannot find module '@babel/core'

babel-watch does not have @babel/core listed as a direct dependency but as a "peerDependency". If you're using babel in your app you should already have @babel/core installed. If not you should do npm install --save-dev @babel/core. We decided not to make @babel/core a direct dependency as in some cases having it defined this way would make your application pull two versions of @babel/core from npm during installation and since @babel/core is quite a huge package that's something we wanted to avoid.

Every time I run a script, I get a load of temporary files clogging up my project root

babel-watch creates a temporary file each time it runs in order to watch for changes. When running as an npm script, this can end up putting these files into your project root. This is due to an issue in npm which changes the value of TMPDIR to the current directory. To fix this, change your npm script from babel-watch ./src/app.js to TMPDIR=/tmp babel-watch ./src/app.js.

I'm getting regeneratorRuntime is not defined error when running with babel-watch but babel-node runs just fine

The reason why you're getting the error is because the babel regenerator plugin (that gives you support for async functions) requires a runtime library to be included with your application. You will get the same error when you build your app with babel first and then run with node. It works fine with babel-node because it includes babel-polyfill module automatically whenever it runs your app, even if you don't use features like async functions (that's one of the reason why its startup time is so long). Please see this answer on stackoverflow to learn how to fix this issue

Still having some issues?

Try searching over the issues on GitHub here. If you don't find anything that would help feel free to open new issue!


All PRs are welcome!