Node CLI

Node JS Platform has a CLI (Command Line Interface) to run basic commands and also script files. When we install Node JS Platform, by default we will get this component. We do not need to any extra configurations for this component.

We can observe “node.exe” file at NODSJS_HOME. It is also known as Node Platform CLI component.

To access Node CLI:

  • Open Command prompt at NODSJS_HOME
  • Run “node.exe” command
  • Now we are able to see NODE CLI i.e. “>”, that means our Node JS Setup is working fine.

We can run basic Java Script commands one by one or entire Java Script files (*.js files) to test the basic functionality.

You can now test pretty much any Node.js/JavaScript expression in Node CLI or REPL. For example, if your write “10 + 20” then it will display result 30 immediately in new line.

> 10 + 20

30

The + operator also concatenates strings as in browser’s JavaScript.

> “Hello” + “World”

Hello World

You can also define variables and perform some operation on them.

> var x = 10, y = 20;

> x + y

30

If you need to write multi line JavaScript expression or function then just press Enter whenever you want to write something in the next line as a continuation of your code. The REPL terminal will display three dots (…), it means you can continue on next line. Write .break to get out of continuity mode.

For example, you can define a function and execute it as shown below.

 

 

You can execute an external JavaScript file by writing node fileName command. For example, assume that node-example.js is on C drive of your PC with following code.

node-example.js

console.log(“Hello World”);

Now, you can execute node-exampel.js from command prompt. To exit from the REPL terminal, press Ctrl + C twice or write .exit and press Enter.

Thus, you can execute any Node.js/JavaScript code in the node shell (REPL). This will give you a result which is similar to the one you will get in the console of Google Chrome browser.

ECMAScript implementation in Node.js and browsers is slightly different. For example, {}+{} is ‘[object Object][object Object]’ in Node.js REPL, whereas the same code is NaN in the Chrome console because of the automatic semicolon insertion feature. However, mostly Node.js REPL and the Chrome/Firefox consoles are similar.

The following table lists important REPL commands.

REPL Command Description
.help Display help on all the commands
tab Keys Display the list of all commands.
Up/Down Keys See previous commands applied in REPL.
.save filename Save current Node REPL session to a file.
.load filename Load the specified file in the current Node REPL session.
ctrl + c Terminate the current command.
ctrl + c (twice) Exit from the REPL.
ctrl + d Exit from the REPL.
.break Exit from multiline expression.
.clear Exit from multiline expression.

 

Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options. To view this documentation as a manual page in a terminal, run man node.

Syntax

node [options] [V8 options] [script.js | -e “script” | -] [–] [arguments]

node inspect [script.js | -e “script” | <host>:<port>] …

node –v8-options

Execute without arguments to start the REPL.

Options

Added in: v8.0.0 Alias for stdin, analogous to the use of – in other command line utilities, meaning that the script will be read from stdin, and the rest of the options are passed to that script.

Added in: v6.11.0 Indicate the end of node options. Pass the rest of the arguments to the script. If no script filename or eval/print script is supplied prior to this, then the next argument will be used as a script filename.

–abort-on-uncaught-exception

Added in: v0.10 Aborting instead of exiting causes a core file to be generated for post-mortem analysis using a debugger (such as lldb, gdb, and mdb).

If this flag is passed, the behavior can still be set to not abort through process.setUncaughtExceptionCaptureCallback() (and through usage of the domain module that uses it).

–completion-bash

Added in: v10.12.0 Print source-able bash completion script for Node.js.

–diagnostic-report-directory=directory

Added in: v11.8.0 Location at which the report will be generated.

–diagnostic-report-filename=filename

Added in: v11.8.0 Name of the file to which the report will be written.

–diagnostic-report-on-fatalerror

Added in: v11.8.0 Enables the report to be triggered on fatal errors (internal errors within the Node.js runtime such as out of memory) that lead to termination of the application, if –experimental-report is enabled. Useful to inspect various diagnostic data elements such as heap, stack, event loop state, resource consumption etc. to reason about the fatal error.

–diagnostic-report-on-signal

Added in: v11.8.0 Enables report to be generated upon receiving the specified (or predefined) signal to the running Node.js process, if –experimental-report is enabled. The signal to trigger the report is specified through –diagnostic-report-signal.

–diagnostic-report-signal=signal

Added in: v11.8.0 Sets or resets the signal for report generation (not supported on Windows). Default signal is SIGUSR2.

–diagnostic-report-uncaught-exception

Added in: v11.8.0 Enables report to be generated on un-caught exceptions, if –experimental-report is enabled. Useful when inspecting JavaScript stack in conjunction with native stack and other runtime environment data.

–diagnostic-report-verbose

Added in: v11.8.0 Flag that enables additional information to be printed during report generation.

–enable-fips

Added in: v6.0.0 Enable FIPS-compliant crypto at startup. (Requires Node.js to be built with ./configure –openssl-fips.)

–experimental-modules

Added in: v8.5.0 Enable experimental ES module support and caching modules.

–experimental-policy

Added in: v11.8.0 Use the specified file as a security policy.

–experimental-repl-await

Added in: v10.0.0 Enable experimental top-level await keyword support in REPL.

–experimental-report

Added in: v11.8.0 Enable experimental diagnostic report feature.

–experimental-vm-modules

Added in: v9.6.0 Enable experimental ES Module support in the vm module.

–force-fips

Added in: v6.0.0 Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.) (Same requirements as –enable-fips.)

–http-parser=library

Added in: v11.4.0 Chooses an HTTP parser library. Available values are: llhttp for https://llhttp.org/ and legacy for https://github.com/nodejs/http-parser

The default is legacy, unless otherwise specified when building Node.js. This flag exists to aid in experimentation with the internal implementation of the Node.js http parser. This flag is likely to become a no-op and removed at some point in the future.

–icu-data-dir=file

Added in: v0.11.15 Specify ICU data load path. (Overrides NODE_ICU_DATA.)

–inspect-brk[=[host:]port]

Added in: v7.6.0 Activate inspector on host:port and break at start of user script. Default host:port is 127.0.0.1:9229.

–inspect-port=[host:]port

Added in: v7.6.0 Set the host:port to be used when the inspector is activated. Useful when activating the inspector by sending the SIGUSR1 signal. Default host is 127.0.0.1.

–inspect[=[host:]port]

Added in: v6.3.0 Activate inspector on host:port. Default is 127.0.0.1:9229. V8 inspector integration allows tools such as Chrome DevTools and IDEs to debug and profile Node.js instances. The tools attach to Node.js instances via a tcp port and communicate using the Chrome DevTools Protocol. Warning: binding inspector to a public IP:port combination is insecure

Binding the inspector to a public IP (including 0.0.0.0) with an open port is insecure, as it allows external hosts to connect to the inspector and perform a remote code execution attack. If you specify a host, make sure that at least one of the following is true: either the host is not public, or the port is properly firewalled to disallow unwanted connections.

More specifically, –inspect=0.0.0.0 is insecure if the port (9229 by default) is not firewall-protected.

–loader=file

Added in: v9.0.0 Specify the file of the custom experimental ECMAScript Module loader.

–max-http-header-size=size

Added in: v11.6.0 Specify the maximum size, in bytes, of HTTP headers. Defaults to 8KB.

–napi-modules

Added in: v7.10.0 This option is a no-op. It is kept for compatibility.

–no-deprecation

Added in: v0.8.0 Silence deprecation warnings.

–no-force-async-hooks-checks

Added in: v9.0.0 Disables runtime checks for async_hooks. These will still be enabled dynamically when async_hooks is enabled.

–no-warnings

Added in: v6.0.0 Silence all process warnings (including deprecations).

–openssl-config=file

Added in: v6.9.0 Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with ./configure –openssl-fips.

–pending-deprecation

Added in: v8.0.0 Emit pending deprecation warnings. Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the –pending-deprecation command line flag, or the NODE_PENDING_DEPRECATION=1 environment variable, is set. Pending deprecations are used to provide a kind of selective “early warning” mechanism that developers may leverage to detect deprecated API usage.

–preserve-symlinks

Added in: v6.3.0 Instructs the module loader to preserve symbolic links when resolving and caching modules. By default, when Node.js loads a module from a path that is symbolically linked to a different on-disk location, Node.js will dereference the link and use the actual on-disk “real path” of the module as both an identifier and as a root path to locate other dependency modules. In most cases, this default behavior is acceptable.

–preserve-symlinks-main

Added in: v10.2.0 Instructs the module loader to preserve symbolic links when resolving and caching the main module (require.main). This flag exists so that the main module can be opted-in to the same behavior that –preserve-symlinks gives to all other imports; they are separate flags, however, for backward compatibility with older Node.js versions.

–prof

Added in: v2.0.0 Generate V8 profiler output.

–prof-process

Added in: v5.2.0 Process V8 profiler output generated using the V8 option –prof.

–redirect-warnings=file

Added in: v8.0.0 Write process warnings to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead.

–throw-deprecation

Added in: v0.11.14 Throw errors for deprecations.

–title=title

Added in: v10.7.0 Set process.title on startup.

–tls-cipher-list=list

Added in: v4.0.0 Specify an alternative default TLS cipher list. Requires Node.js to be built with crypto support (default).

–trace-deprecation

Added in: v0.8.0 Print stack traces for deprecations.

–trace-event-categories

Added in: v7.7.0 A comma separated list of categories that should be traced when trace event tracing is enabled using –trace-events-enabled.

–trace-event-file-pattern

Added in: v9.8.0 Template string specifying the filepath for the trace event data, it supports ${rotation} and ${pid}.

–trace-events-enabled

Added in: v7.7.0 Enables the collection of trace event tracing information.

–trace-sync-io

Added in: v2.1.0 Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop.

–trace-warnings

Added in: v6.0.0 Print stack traces for process warnings (including deprecations).

–track-heap-objects

Added in: v2.4.0 Track heap object allocations for heap snapshots.

`–use-bundled-ca`, `–use-openssl-ca`

Added in: v6.11.0 Use bundled Mozilla CA store as supplied by current Node.js version or use OpenSSL’s default CA store. The default store is selectable at build-time. The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms. Using OpenSSL store allows for external modifications of the store. For most Linux and BSD distributions, this store is maintained by the distribution maintainers and system administrators. OpenSSL CA store location is dependent on configuration of the OpenSSL library but this can be altered at runtime using environment variables.

–v8-options

Added in: v0.1.3 Print V8 command line options.

–v8-pool-size=num

Added in: v5.10.0 Set V8’s thread pool size which will be used to allocate background jobs. If set to 0 then V8 will choose an appropriate size of the thread pool based on the number of online processors. If the value provided is larger than V8’s maximum, then the largest value will be chosen.

`-c`, `–check`

Syntax check the script without executing.

`-e`, `–eval “script”`

Evaluate the following argument as JavaScript. The modules which are predefined in the REPL can also be used in script. On Windows, using cmd.exe a single quote will not work correctly because it only recognizes double ” for quoting. In Powershell or Git bash, both ‘ and ” are usable.

`-h`, `–help`

Added in: v0.1.3 Print node command line options. The output of this option is less detailed than this document.

`-i`, `–interactive`

Added in: v0.7.7 Opens the REPL even if stdin does not appear to be a terminal.

`-p`, `–print “script”`

Identical to -e but prints the result.

`-r`, `–require module`

Added in: v1.6.0 Preload the specified module at startup. Follows require()’s module resolution rules. module may be either a path to a file, or a node module name.

`-v`, `–version`

Added in: v0.1.3 Print node’s version.

Environment Variables

NODE_DEBUG=module[,…]

Added in: v0.1.32 ‘,’-separated list of core modules that should print debug information.

NODE_DEBUG_NATIVE=module[,…]

‘,’-separated list of core C++ modules that should print debug information.

NODE_DISABLE_COLORS=1

Added in: v0.3.0 When set to 1 colors will not be used in the REPL.

NODE_EXTRA_CA_CERTS=file

Added in: v7.3.0 When set, the well known “root” CAs (like VeriSign) will be extended with the extra certificates in file. The file should consist of one or more trusted certificates in PEM format. A message will be emitted (once) with process.emitWarning() if the file is missing or malformed, but any errors are otherwise ignored.

NODE_ICU_DATA=file

Added in: v0.11.15 Data path for ICU (Intl object) data. Will extend linked-in data when compiled with small-icu support.

NODE_NO_WARNINGS=1

Added in: v6.11.0 When set to 1, process warnings are silenced.

NODE_OPTIONS=options…

Added in: v8.0.0 A space-separated list of command line options. options… are interpreted as if they had been specified on the command line before the actual command line (so they can be overridden). Node.js will exit with an error if an option that is not allowed in the environment is used, such as -p or a script file.

NODE_PATH=path[:…]

Added in: v0.1.32 ‘:’-separated list of directories prefixed to the module search path. On Windows, this is a ‘;’-separated list instead.

NODE_PENDING_DEPRECATION=1

Added in: v8.0.0 When set to 1, emit pending deprecation warnings. Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the –pending-deprecation command line flag, or the NODE_PENDING_DEPRECATION=1 environment variable, is set. Pending deprecations are used to provide a kind of selective “early warning” mechanism that developers may leverage to detect deprecated API usage.

NODE_PRESERVE_SYMLINKS=1

Added in: v7.1.0 When set to 1, instructs the module loader to preserve symbolic links when resolving and caching modules.

NODE_REDIRECT_WARNINGS=file

Added in: v8.0.0 When set, process warnings will be emitted to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead. This is equivalent to using the –redirect-warnings=file command-line flag.

NODE_REPL_HISTORY=file

Added in: v3.0.0 Path to the file used to store the persistent REPL history. The default path is ~/.node_repl_history, which is overridden by this variable. Setting the value to an empty string (” or ‘ ‘) disables persistent REPL history.

NODE_TLS_REJECT_UNAUTHORIZED=value

If value equals ‘0’, certificate validation is disabled for TLS connections. This makes TLS, and HTTPS by extension, insecure. The use of this environment variable is strongly discouraged.

NODE_V8_COVERAGE=dir

When set, Node.js will begin outputting V8 JavaScript code coverage to the directory provided as an argument. Coverage is output as an array of ScriptCoverage objects. NODE_V8_COVERAGE will automatically propagate to subprocesses, making it easier to instrument applications that call the child_process.spawn() family of functions. NODE_V8_COVERAGE can be set to an empty string, to prevent propagation. At this time coverage is only collected in the main thread and will not be output for code executed by worker threads.

OPENSSL_CONF=file

Added in: v6.11.0 Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with ./configure –openssl-fips. If the –openssl-config command line option is used, the environment variable is ignored.

SSL_CERT_DIR=dir

Added in: v7.7.0 If –use-openssl-ca is enabled, this overrides and sets OpenSSL’s directory containing trusted certificates. Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

SSL_CERT_FILE=file

Added in: v7.7.0 If –use-openssl-ca is enabled, this overrides and sets OpenSSL’s file containing trusted certificates. Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

UV_THREADPOOL_SIZE=size

Set the number of threads used in libuv’s threadpool to size threads. Asynchronous system APIs are used by Node.js whenever possible, but where they do not exist, libuv’s threadpool is used to create asynchronous node APIs based on synchronous system APIs. Node.js APIs that use the threadpool are:

  • all fs APIs, other than the file watcher APIs and those that are explicitly synchronous
  • pbkdf2()
  • randomBytes(), unless it is used without a callback
  • randomFill()
  • lookup()
  • all zlib APIs, other than those that are explicitly synchronous

Because libuv’s threadpool has a fixed size, it means that if for whatever reason any of these APIs takes a long time, other (seemingly unrelated) APIs that run in libuv’s threadpool will experience degraded performance. In order to mitigate this issue, one potential solution is to increase the size of libuv’s threadpool by setting the ‘UV_THREADPOOL_SIZE’ environment variable to a value greater than 4 (its current default value).

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