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interface

Console

interface Console

  • [Symbol.asyncIterator](): AsyncIterableIterator<string>;

    Asynchronously read lines from standard input (fd 0)

    for await (const line of console) {
  console.log(line);
}
  • condition?: boolean,
    ...data: any[]
    ): void;
    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
    @param value

    The value tested for being truthy.

    @param message

    All arguments besides value are used as error message.

  • 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.

  • 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
>
    @param label

    The display label for the counter.

  • 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
>
    @param label

    The display label for the counter.

  • ...data: any[]
    ): void;
    message?: any,
    ...optionalParams: any[]
    ): void;

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

  • item?: any,
    options?: any
    ): void;
    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.

  • ...data: any[]
    ): void;

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

  • ...data: any[]
    ): void;

    Log to stderr in your terminal

    Appears in red

    @param data

    something to display

    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.

  • ...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.

  • ...label: any[]
    ): void;

    An alias for group.

  • groupEnd(): void;

    Decreases indentation of subsequent lines by spaces for groupIndentation length.

  • ...data: any[]
    ): void;
    message?: any,
    ...optionalParams: any[]
    ): void;

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

  • ...data: any[]
    ): void;
    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.

  • 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.
  • 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.

  • tabularData?: any,
    properties?: 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 }]);
// ┌────┬─────┬─────┐
// │    │  a  │  b  │
// ├────┼─────┼─────┤
// │  0 │  1  │ 'Y' │
// │  1 │ 'Z' │  2  │
// └────┴─────┴─────┘

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

    Alternate properties for constructing the 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' │
// └─────────┴─────┘
    @param properties

    Alternate properties for constructing the table.

  • 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".

  • 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
  • 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');
  • 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.

  • ...data: any[]
    ): void;
    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)
  • ...data: any[]
    ): void;
    message?: any,
    ...optionalParams: any[]
    ): void;

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

  • ...data: string | ArrayBuffer | ArrayBufferView<ArrayBufferLike>[]
    ): number;

    Write text or bytes to stdout

    Unlike console.log, this does no formatting and doesn't add a newline or spaces between arguments. You can pass it strings or bytes or any combination of the two.

    console.write("hello world!", "\n"); // "hello world\n"
    @param data

    The data to write

    @returns

    The number of bytes written

    This function is not available in the browser.