CLI

Babel comes with a built-in CLI which can be used to compile files from the command line.

Installation

While you can install Babel CLI globally on your machine, it’s much better to install it locally project by project.

There are two primary reasons for this.

1. Different projects on the same machine can depend on different versions of Babel allowing you to update one at a time.
2. It means you do not have an implicit dependency on the environment you are working in. Making your project far more portable and easier to setup.

We can install Babel CLI locally by running:

npm install --save-dev babel-cli

Note: If you do not have a package.json, create one before installing. This will ensure proper interaction with the npx command.

After that finishes installing, your package.json file should include:

{
  "devDependencies": {
+   "babel-cli": "^6.0.0"
  }
}

babel

Note: These instructions use the excellent npx command to run the locally installed executables. You can drop it inside of an npm run script or you may instead execute with the relative path instead. ./node_modules/.bin/babel

Compile Files

Compile the file script.js and output to stdout.

npx babel script.js
# output...

If you would like to output to a file you may use --out-file or -o.

npx babel script.js --out-file script-compiled.js

To compile a file every time that you change it, use the --watch or -w option:

npx babel script.js --watch --out-file script-compiled.js

Compile with Source Maps

If you would then like to add a source map file you can use --source-maps or -s. Learn more about source maps.

npx babel script.js --out-file script-compiled.js --source-maps

If you would rather have inline source maps, you may use --source-maps inline.

npx babel script.js --out-file script-compiled.js --source-maps inline

Compile Directories

Compile the entire src directory and output it to the lib directory. You may use --out-dir or -d. This doesn’t overwrite any other files or directories in lib.

npx babel src --out-dir lib

Compile the entire src directory and output it to the one concatenated file.

npx babel src --out-file script-compiled.js

Ignore files

Ignore spec and test files

npx babel src --out-dir lib --ignore spec.js,test.js

Copy files

Copy files that will not be compiled

npx babel src --out-dir lib --copy-files

Piping Files

Pipe a file in via stdin and output it to script-compiled.js

npx babel --out-file script-compiled.js < script.js

Using Plugins

Use the --plugins option to specify plugins to use in compilation

npx babel script.js --out-file script-compiled.js --plugins=transform-runtime,transform-es2015-modules-amd

Using Presets

Use the --presets option to specify plugins to use in compilation

npx babel script.js --out-file script-compiled.js --presets=es2015,react

Ignoring .babelrc

Ignore the configuration from the projects .babelrc file and use the cli options e.g. for a custom build

npx babel --no-babelrc script.js --out-file script-compiled.js --presets=es2015,react

Advanced Usage

There are many more options available in the babel CLI, see options, babel --help and other sections for more information.

babel-node

Not meant for production use

You should not be using babel-node in production. It is unnecessarily heavy, with high memory usage due to the cache being stored in memory. You will also always experience a startup performance penalty as the entire app needs to be compiled on the fly.

Check out the example Node.js server with Babel for an idea of how to use Babel in a production deployment.

ES6-style module-loading may not function as expected

Due to technical limitations ES6-style module-loading is not fully supported in a babel-node REPL.

babel comes with a second CLI which works exactly the same as Node.js’s CLI, only it will compile ES6 code before running it.

Launch a REPL (Read-Eval-Print-Loop).

npx babel-node

Evaluate code.

npx babel-node -e "class Test { }"

Compile and run test.js.

npx babel-node test

Tip: Use rlwrap to get a REPL with input history

npx rlwrap babel-node

On some platforms (like OSX), extra arguments may be required for rlwrap to function properly, eg:

NODE_NO_READLINE=1 npx rlwrap --always-readline babel-node

Usage

babel-node [options] [ -e script | script.js ] [arguments]

When arguments for user script have names conflicting with node options, double dash placed before script name can be used to resolve ambiguities

npx babel-node --debug --presets es2015 -- script.js --debug

Options