Node.js's command-line tools

The basic installation of Node.js includes two commands, node and npm. We've already seen the node command in action. It's used either for running command-line scripts or server processes. The other, npm, is a package manager for Node.js.

The easiest way to verify that your Node.js installation works is also the best way to get help with Node.js. Type the following command:

$ node --help
Usage: node [options] [ -e script | script.js | - ] [arguments]
       node inspect script.js [arguments]

Options:
  -v, --version print Node.js version
  -e, --eval script evaluate script
  -p, --print evaluate script and print result
  -c, --check syntax check script without executing
  -i, --interactive always enter the REPL even if stdin
                             does not appear to be a terminal
  -r, --require module to preload (option can be repeated)
  - script read from stdin (default; interactive mode if a tty)
  --inspect[=[host:]port] activate inspector on host:port
                             (default: 127.0.0.1:9229)
  --inspect-brk[=[host:]port]
                             activate inspector on host:port
                             and break at start of user script
  --inspect-port=[host:]port
                             set host:port for inspector

... many more options
Environment variables:
NODE_DEBUG ','-separated list of core modules
                             that should print debug information
NODE_DISABLE_COLORS set to 1 to disable colors in the REPL
NODE_EXTRA_CA_CERTS path to additional CA certificates
                             file
NODE_ICU_DATA data path for ICU (Intl object) data
                             (will extend linked-in data)
NODE_NO_WARNINGS set to 1 to silence process warnings
NODE_NO_HTTP2 set to 1 to suppress the http2 module
NODE_OPTIONS set CLI options in the environment
                             via a space-separated list
NODE_PATH ':'-separated list of directories
                             prefixed to the module search path
NODE_PENDING_DEPRECATION set to 1 to emit pending deprecation
                             warnings
NODE_REPL_HISTORY path to the persistent REPL history
                             file
NODE_REDIRECT_WARNINGS write warnings to path instead of
                             stderr
OPENSSL_CONF load OpenSSL configuration from file

Documentation can be found at https://nodejs.org/

Note that there are options for both Node.js and V8 (not shown in the previous command line). Remember that Node.js is built on top of V8; it has its own universe of options that largely focus on details of bytecode compilation or garbage collection and heap algorithms. Enter node --v8-options to see the full list of them.

On the command line, you can specify options, a single script file, and a list of arguments to that script. We'll discuss script arguments further in the next section, Running a simple script with Node.js.

Running Node.js with no arguments plops you into an interactive JavaScript shell:

$ node
> console.log('Hello, world!');
Hello, world!
undefined  

Any code you can write in a Node.js script can be written here. The command interpreter gives a good Terminal-oriented user experience and is useful for interactively playing with your code. You do play with your code, don't you? Good!