- Assertion Testing
- Async Hooks
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- C++ Addons
- C/C++ Addons - N-API
- Child Processes
- Cluster
- Command Line Options
- Console
- Crypto
- Debugger
- Deprecated APIs
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- Performance Hooks
- Process
- Punycode
- Query Strings
- Readline
- REPL
- Stream
- String Decoder
- Timers
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- TTY
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- Utilities
- V8
- VM
- Worker Threads
- Zlib
Node.js v10.20.2-test20200417ef2df6986b Documentation
Table of Contents
-
-
- new Console(stdout[, stderr][, ignoreErrors])
- new Console(options)
- console.assert(value[, ...message])
- console.clear()
- console.count([label])
- console.countReset([label])
- console.debug(data[, ...args])
- console.dir(obj[, options])
- console.dirxml(...data)
- console.error([data][, ...args])
- console.group([...label])
- console.groupCollapsed()
- console.groupEnd()
- console.info([data][, ...args])
- console.log([data][, ...args])
- console.table(tabularData[, properties])
- console.time([label])
- console.timeEnd([label])
- console.timeLog([label][, ...data])
- console.trace([message][, ...args])
- console.warn([data][, ...args])
-
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 asconsole.log()
,console.error()
andconsole.warn()
that can be used to write to any Node.js stream. - A global
console
instance configured to write toprocess.stdout
andprocess.stderr
. The globalconsole
can be used without callingrequire('console')
.
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: Whoops, something bad happened], to stderr
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
Class: Console#
The Console
class can be used to create a simple logger with configurable
output streams and can be accessed using either require('console').Console
or console.Console
(or their destructured counterparts):
const { Console } = require('console');
const { Console } = console;
new Console(stdout[, stderr][, ignoreerrors])#
new Console(options)#
-
options
<Object>stdout
<stream.Writable>stderr
<stream.Writable>ignoreErrors
<boolean> Ignore errors when writing to the underlying streams. Default:true
.colorMode
<boolean> | <string> Set color support for thisConsole
instance. Setting totrue
enables coloring while inspecting values, setting to'auto'
will make color support depend on the value of theisTTY
property and the value returned bygetColorDepth()
on the respective stream. Default:'auto'
.
Creates a new Console
with one or two writable stream instances. stdout
is a
writable stream to print log or info output. stderr
is used for warning or
error output. If stderr
is not provided, stdout
is used for stderr
.
const output = fs.createWriteStream('./stdout.log');
const errorOutput = fs.createWriteStream('./stderr.log');
// custom simple logger
const logger = new Console({ stdout: output, stderr: errorOutput });
// use it like console
const count = 5;
logger.log('count: %d', count);
// in stdout.log: count 5
The global console
is a special Console
whose output is sent to
process.stdout
and process.stderr
. It is equivalent to calling:
new Console({ stdout: process.stdout, stderr: process.stderr });
console.assert(value[, ...message])[src]#
value
<any> The value tested for being truthy....message
<any> All arguments besidesvalue
are used as error message.
A simple assertion test that verifies whether value
is truthy. If it is not,
Assertion failed
is logged. If provided, the error message
is formatted
using util.format()
by passing along all message arguments. The output is
used as the error message.
console.assert(true, 'does nothing');
// OK
console.assert(false, 'Whoops %s work', 'didn\'t');
// Assertion failed: Whoops didn't work
Calling console.assert()
with a falsy assertion will only cause the message
to be printed to the console without interrupting execution of subsequent code.
console.clear()[src]#
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.
console.count([label])[src]#
label
<string> The display label for the counter. Default:'default'
.
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
>
console.countReset([label])[src]#
label
<string> The display label for the counter. Default:'default'
.
Resets the internal counter specific to label
.
> console.count('abc');
abc: 1
undefined
> console.countReset('abc');
undefined
> console.count('abc');
abc: 1
undefined
>
console.debug(data[, ...args])[src]#
The console.debug()
function is an alias for console.log()
.
console.dir(obj[, options])[src]#
obj
<any>-
options
<Object>showHidden
<boolean> Iftrue
then the object's non-enumerable and symbol properties will be shown too. Default:false
.depth
<number> Tellsutil.inspect()
how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. To make it recurse indefinitely, passnull
. Default:2
.colors
<boolean> Iftrue
, then the output will be styled with ANSI color codes. Colors are customizable; see customizingutil.inspect()
colors. Default:false
.
Uses util.inspect()
on obj
and prints the resulting string to stdout
.
This function bypasses any custom inspect()
function defined on obj
.
console.dirxml(...data)[src]#
...data
<any>
This method calls console.log()
passing it the arguments received.
Please note that this method does not produce any XML formatting.
console.error([data][, ...args])[src]#
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.
console.group([...label])[src]#
...label
<any>
Increases indentation of subsequent lines by two spaces.
If one or more label
s are provided, those are printed first without the
additional indentation.
console.groupCollapsed()[src]#
An alias for console.group()
.
console.groupEnd()[src]#
Decreases indentation of subsequent lines by two spaces.
console.info([data][, ...args])[src]#
The console.info()
function is an alias for console.log()
.
console.log([data][, ...args])[src]#
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.
console.table(tabularData[, properties])[src]#
tabularData
<any>properties
<string[]> Alternate properties for constructing the table.
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' │
// └─────────┴─────┘
console.time([label])[src]#
label
<string> Default:'default'
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
console.timeEnd()
to stop the timer and output the elapsed time in
milliseconds to stdout
. Timer durations are accurate to the sub-millisecond.
console.timeEnd([label])[src]#
label
<string> Default:'default'
Stops a timer that was previously started by calling console.time()
and
prints the result to stdout
:
console.time('100-elements');
for (let i = 0; i < 100; i++) {}
console.timeEnd('100-elements');
// prints 100-elements: 225.438ms
console.timeLog([label][, ...data])[src]#
For a timer that was previously started by calling console.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');
console.trace([message][, ...args])[src]#
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)
console.warn([data][, ...args])[src]#
The console.warn()
function is an alias for console.error()
.
Inspector only methods#
The following methods are exposed by the V8 engine in the general API but do
not display anything unless used in conjunction with the inspector
(--inspect
flag).
console.markTimeline([label])#
label
<string> Default:'default'
This method does not display anything unless used in the inspector. The
console.markTimeline()
method is the deprecated form of
console.timeStamp()
.
console.profile([label])#
label
<string>
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 console.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.
console.profileEnd([label])#
label
<string>
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
console.profile()
for an example.
If this method is called without a label, the most recently started profile is stopped.
console.timeStamp([label])#
label
<string>
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.
console.timeline([label])#
label
<string> Default:'default'
This method does not display anything unless used in the inspector. The
console.timeline()
method is the deprecated form of console.time()
.
console.timelineEnd([label])#
label
<string> Default:'default'
This method does not display anything unless used in the inspector. The
console.timelineEnd()
method is the deprecated form of
console.timeEnd()
.