Clack is a modern, flexible and powerful CLI library that helps you build beautiful command-line interfaces with ease. It provides a set of high-level components and low-level primitives that make it simple to create interactive command-line applications.
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = newconsole.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
NodeJS.Process.exit(code?: number | string |null|undefined): never
The process.exit() method instructs Node.js to terminate the process
synchronously with an exit status of code. If code is omitted, exit uses
either the 'success' code 0 or the value of process.exitCode if it has been
set. Node.js will not terminate until all the 'exit' event listeners are
called.
To exit with a 'failure' code:
import { exit } from'node:process';
exit(1);
The shell that executed Node.js should see the exit code as 1.
Calling process.exit() will force the process to exit as quickly as possible
even if there are still asynchronous operations pending that have not yet
completed fully, including I/O operations to process.stdout and process.stderr.
In most situations, it is not actually necessary to call process.exit() explicitly. The Node.js process will exit on its own if there is no additionalwork pending in the event loop. The process.exitCode property can be set to
tell the process which exit code to use when the process exits gracefully.
For instance, the following example illustrates a misuse of the process.exit() method that could lead to data printed to stdout being
truncated and lost:
import { exit } from'node:process';
// This is an example of what *not* to do:
if (someConditionNotMet()) {
printUsageToStdout();
exit(1);
}
The reason this is problematic is because writes to process.stdout in Node.js
are sometimes asynchronous and may occur over multiple ticks of the Node.js
event loop. Calling process.exit(), however, forces the process to exit before those additional writes to stdout can be performed.
Rather than calling process.exit() directly, the code should set the process.exitCode and allow the process to exit naturally by avoiding
scheduling any additional work for the event loop:
import process from'node:process';
// How to properly set the exit code while letting
// the process exit gracefully.
if (someConditionNotMet()) {
printUsageToStdout();
process.exitCode=1;
}
If it is necessary to terminate the Node.js process due to an error condition,
throwing an uncaught error and allowing the process to terminate accordingly
is safer than calling process.exit().
In Worker threads, this function stops the current thread rather
than the current process.
@since ― v0.1.13
@param ― code The exit code. For string type, only integer strings (e.g.,'1') are allowed.
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.
Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(newError('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
// Error: Whoops, something bad happened
// at [eval]:5:15
// at Script.runInThisContext (node:vm:132:18)
// at Object.runInThisContext (node:vm:309:38)
// at node:internal/process/execution:77:19
// at [eval]-wrapper:6:22
// at evalScript (node:internal/process/execution:76:60)
// at node:internal/main/eval_string:23:3
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = newconsole.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(newError('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
NodeJS.Process.exit(code?: number | string |null|undefined): never
The process.exit() method instructs Node.js to terminate the process
synchronously with an exit status of code. If code is omitted, exit uses
either the 'success' code 0 or the value of process.exitCode if it has been
set. Node.js will not terminate until all the 'exit' event listeners are
called.
To exit with a 'failure' code:
import { exit } from'node:process';
exit(1);
The shell that executed Node.js should see the exit code as 1.
Calling process.exit() will force the process to exit as quickly as possible
even if there are still asynchronous operations pending that have not yet
completed fully, including I/O operations to process.stdout and process.stderr.
In most situations, it is not actually necessary to call process.exit() explicitly. The Node.js process will exit on its own if there is no additionalwork pending in the event loop. The process.exitCode property can be set to
tell the process which exit code to use when the process exits gracefully.
For instance, the following example illustrates a misuse of the process.exit() method that could lead to data printed to stdout being
truncated and lost:
import { exit } from'node:process';
// This is an example of what *not* to do:
if (someConditionNotMet()) {
printUsageToStdout();
exit(1);
}
The reason this is problematic is because writes to process.stdout in Node.js
are sometimes asynchronous and may occur over multiple ticks of the Node.js
event loop. Calling process.exit(), however, forces the process to exit before those additional writes to stdout can be performed.
Rather than calling process.exit() directly, the code should set the process.exitCode and allow the process to exit naturally by avoiding
scheduling any additional work for the event loop:
import process from'node:process';
// How to properly set the exit code while letting
// the process exit gracefully.
if (someConditionNotMet()) {
printUsageToStdout();
process.exitCode=1;
}
If it is necessary to terminate the Node.js process due to an error condition,
throwing an uncaught error and allowing the process to terminate accordingly
is safer than calling process.exit().
In Worker threads, this function stops the current thread rather
than the current process.
@since ― v0.1.13
@param ― code The exit code. For string type, only integer strings (e.g.,'1') are allowed.
exit(0);
}
Next Steps
Check out our Examples for more practical use cases
Clack is built with TypeScript and provides full type safety. All components and primitives are properly typed, making it easy to catch errors at compile time.
@param ― string A string to convert into a number.
@param ― radix A value between 2 and 36 that specifies the base of the number in string.
If this argument is not supplied, strings with a prefix of '0x' are considered hexadecimal.
All other strings are considered decimal.
parseInt(
value: string
value);
if (
functionisNaN(number:number):boolean
Returns a Boolean value that indicates whether a value is the reserved value NaN (not a number).
@param ― number A numeric value.
isNaN(
const num:number
num)) return 'Please enter a valid number';
if (
const num:number
num < 0 ||
const num:number
num > 120) return 'Age must be between 0 and 120';
return
var undefined
undefined;
},
});
Contributing
We welcome contributions! Please check out our Contributing Guide for details on our code of conduct and the process for submitting pull requests.
