ConstOptionalcondition: booleanconsole.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
The value tested for being truthy.
Optionalmessage: stringAll arguments besides value are used as error message.
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.
Optionallabel: stringMaintains 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
>
Optionallabel: stringThe display label for the counter.
Optionallabel: stringResets the internal counter specific to label.
> console.count('abc');
abc: 1
undefined
> console.countReset('abc');
undefined
> console.count('abc');
abc: 1
undefined
>
Optionallabel: stringThe display label for the counter.
Optionalitem: anyOptionaloptions: anyUses util.inspect() on obj and prints the resulting string to stdout.
This function bypasses any custom inspect() function defined on obj.
Optionaloptions: InspectOptionsPrints 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.
Optionalmessage: anyIncreases indentation of subsequent lines by spaces for groupIndentation length.
If one or more labels are provided, those are printed first without the
additional indentation.
An alias for group.
The console.info() function is an alias for log.
Optionalmessage: anyPrints 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.
Optionalmessage: anyThis 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.
Optionallabel: stringThis 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.
Optionallabel: stringOptionaltabularData: anyOptionalproperties: string[]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' │
// └─────────┴─────┘
Optionalproperties: readonly string[]Alternate properties for constructing the table.
Optionallabel: stringStarts 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".
Optionallabel: stringOptionallabel: stringStops 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
Optionallabel: stringOptionallabel: stringFor 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');
Optionallabel: stringOptionallabel: stringThis 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.
Optionallabel: stringPrints 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)
Optionalmessage: anyThe console.warn() function is an alias for error.
Optionalmessage: any
Logger preset with debug messages suppressed