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console

The node: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(new Error('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 = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err

Usage in Deno

import * as mod from "node:console";

Interfaces

I
console.ConsoleConstructor
No documentation available

Namespaces

N
v
console

The console module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers.

    interface Console

    Usage in Deno

    import { type Console } from "node:console";

    Properties #

    Methods #

    #assert(
    value: any,
    message?: string,
    ...optionalParams: any[],
    ): void

    console.assert() writes a message if value is falsy or omitted. It only writes a message and does not otherwise affect execution. The output always starts with "Assertion failed". If provided, message is formatted using util.format().

    If value is truthy, nothing happens.

    console.assert(true, 'does nothing');

console.assert(false, 'Whoops %s work', 'didn\'t');
// Assertion failed: Whoops didn't work

console.assert();
// Assertion failed
    #clear(): void

    When stdout is a TTY, calling console.clear() will attempt to clear the TTY. When stdout is not a TTY, this method does nothing.

    The specific operation of console.clear() can vary across operating systems and terminal types. For most Linux operating systems, console.clear() operates similarly to the clear shell command. On Windows, console.clear() will clear only the output in the current terminal viewport for the Node.js binary.

    #count(label?: string): void

    Maintains an internal counter specific to label and outputs to stdout the number of times console.count() has been called with the given label.

    > console.count()
default: 1
undefined
> console.count('default')
default: 2
undefined
> console.count('abc')
abc: 1
undefined
> console.count('xyz')
xyz: 1
undefined
> console.count('abc')
abc: 2
undefined
> console.count()
default: 3
undefined
>
    #countReset(label?: string): void

    Resets the internal counter specific to label.

    > console.count('abc');
abc: 1
undefined
> console.countReset('abc');
undefined
> console.count('abc');
abc: 1
undefined
>
    #debug(
    message?: any,
    ...optionalParams: any[],
    ): void

    The console.debug() function is an alias for log.

    #dir(
    obj: any,
    options?: InspectOptions,
    ): void

    Uses util.inspect() on obj and prints the resulting string to stdout. This function bypasses any custom inspect() function defined on obj.

    #dirxml(...data: any[]): void

    This method calls console.log() passing it the arguments received. This method does not produce any XML formatting.

    #error(
    message?: any,
    ...optionalParams: any[],
    ): void

    Prints to stderr 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()).

    const code = 5;
console.error('error #%d', code);
// Prints: error #5, to stderr
console.error('error', code);
// Prints: error 5, to stderr

    If formatting elements (e.g. %d) are not found in the first string then util.inspect() is called on each argument and the resulting string values are concatenated. See util.format() for more information.

    #group(...label: any[]): void

    Increases indentation of subsequent lines by spaces for groupIndentation length.

    If one or more labels are provided, those are printed first without the additional indentation.

    #groupCollapsed(...label: any[]): void

    An alias for group.

    #groupEnd(): void

    Decreases indentation of subsequent lines by spaces for groupIndentation length.

    #info(
    message?: any,
    ...optionalParams: any[],
    ): void

    The console.info() function is an alias for log.

    #log(
    message?: any,
    ...optionalParams: any[],
    ): void

    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()).

    const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout

    See util.format() for more information.

    #table(
    tabularData: any,
    properties?: readonly string[],
    ): void

    Try to construct a table with the columns of the properties of tabularData (or use properties) and rows of tabularData and log it. Falls back to just logging the argument if it can't be parsed as tabular.

    // These can't be parsed as tabular data
console.table(Symbol());
// Symbol()

console.table(undefined);
// undefined

console.table([{ a: 1, b: 'Y' }, { a: 'Z', b: 2 }]);
// ┌─────────┬─────┬─────┐
// │ (index) │  a  │  b  │
// ├─────────┼─────┼─────┤
// │    0    │  1  │ 'Y' │
// │    1    │ 'Z' │  2  │
// └─────────┴─────┴─────┘

console.table([{ a: 1, b: 'Y' }, { a: 'Z', b: 2 }], ['a']);
// ┌─────────┬─────┐
// │ (index) │  a  │
// ├─────────┼─────┤
// │    0    │  1  │
// │    1    │ 'Z' │
// └─────────┴─────┘
    #time(label?: string): void

    Starts a timer that can be used to compute the duration of an operation. Timers are identified by a unique label. Use the same label when calling timeEnd to stop the timer and output the elapsed time in suitable time units to stdout. For example, if the elapsed time is 3869ms, console.timeEnd() displays "3.869s".

    #timeEnd(label?: string): void

    Stops a timer that was previously started by calling time and prints the result to stdout:

    console.time('bunch-of-stuff');
// Do a bunch of stuff.
console.timeEnd('bunch-of-stuff');
// Prints: bunch-of-stuff: 225.438ms
    #timeLog(
    label?: string,
    ...data: any[],
    ): void

    For a timer that was previously started by calling time, prints the elapsed time and other data arguments to stdout:

    console.time('process');
const value = expensiveProcess1(); // Returns 42
console.timeLog('process', value);
// Prints "process: 365.227ms 42".
doExpensiveProcess2(value);
console.timeEnd('process');
    #trace(
    message?: any,
    ...optionalParams: any[],
    ): void

    Prints to stderr the string 'Trace: ', followed by the util.format() formatted message and stack trace to the current position in the code.

    console.trace('Show me');
// Prints: (stack trace will vary based on where trace is called)
//  Trace: Show me
//    at repl:2:9
//    at REPLServer.defaultEval (repl.js:248:27)
//    at bound (domain.js:287:14)
//    at REPLServer.runBound [as eval] (domain.js:300:12)
//    at REPLServer.<anonymous> (repl.js:412:12)
//    at emitOne (events.js:82:20)
//    at REPLServer.emit (events.js:169:7)
//    at REPLServer.Interface._onLine (readline.js:210:10)
//    at REPLServer.Interface._line (readline.js:549:8)
//    at REPLServer.Interface._ttyWrite (readline.js:826:14)
    #warn(
    message?: any,
    ...optionalParams: any[],
    ): void

    The console.warn() function is an alias for error.

    #profile(label?: string): void

    This method does not display anything unless used in the inspector. The console.profile() method starts a JavaScript CPU profile with an optional label until profileEnd is called. The profile is then added to the Profile panel of the inspector.

    console.profile('MyLabel');
// Some code
console.profileEnd('MyLabel');
// Adds the profile 'MyLabel' to the Profiles panel of the inspector.
    #profileEnd(label?: string): void

    This method does not display anything unless used in the inspector. Stops the current JavaScript CPU profiling session if one has been started and prints the report to the Profiles panel of the inspector. See profile for an example.

    If this method is called without a label, the most recently started profile is stopped.

    #timeStamp(label?: string): void

    This method does not display anything unless used in the inspector. The console.timeStamp() method adds an event with the label 'label' to the Timeline panel of the inspector.

    interface console.ConsoleConstructorOptions

    Usage in Deno

    import { console } from "node:console";

    Properties #

    #stdout: WritableStream
    #stderr: WritableStream | undefined
    optional
    #ignoreErrors: boolean | undefined
    optional

    Ignore errors when writing to the underlying streams.

    #colorMode:
    boolean
    | "auto"
    | undefined
    optional

    Set color support for this Console instance. Setting to true enables coloring while inspecting values. Setting to false disables coloring while inspecting values. Setting to 'auto' makes color support depend on the value of the isTTY property and the value returned by getColorDepth() on the respective stream. This option can not be used, if inspectOptions.colors is set as well.

    #inspectOptions: InspectOptions | undefined
    optional

    Specifies options that are passed along to util.inspect().

    #groupIndentation: number | undefined
    optional

    Set group indentation.

    namespace console

    Usage in Deno

    import { console } from "node:console";

    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(new Error('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 = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err

    Interfaces #

    I
    console.ConsoleConstructor
    No documentation available

    See #

    variable console

    Type #

    Console

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