Debugging

When debugging complex pipelines, you need to see what's happening at each step. The inspect and inspectError functions let you peek at values without affecting the flow.

inspect - Peek at Success Values

inspect runs a side effect function on success values but always returns the original result unchanged:

import { 
import Result
Result
} from '@praha/byethrow';
const
const result: Result.Result<number, never>
result
=
import Result
Result
.
const pipe: <Result.Result<42, never>, Result.Result<42, never>, Result.Result<number, never>>(a: Result.Result<42, never>, ab: (a: Result.Result<42, never>) => Result.Result<42, never>, bc: (b: Result.Result<42, never>) => Result.Result<number, never>) => Result.Result<number, never> (+25 overloads)
pipe
(
import Result
Result
.
const succeed: <42>(value: 42) => Result.Result<42, never> (+1 overload)
succeed
(42),
import Result
Result
.
const inspect: <Result.Result<42, never>, void>(fn: (a: 42) => void) => (result: Result.Result<42, never>) => Result.Result<42, never> (+1 overload)
inspect
((
value: 42
value
) =>
var console: 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
@seesource
console
.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)

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.

@sincev0 .1.100
log
('Value:',
value: 42
value
)),
import Result
Result
.
const map: <Result.Result<42, never>, number>(fn: (a: 42) => number) => (result: Result.Result<42, never>) => Result.Result<number, never> (+1 overload)
map
((
x: 42
x
) =>
x: 42
x
* 2),
); // Console: "Value: 42" // { type: 'Success', value: 84 }

On failure, inspect does nothing:

import { 
import Result
Result
} from '@praha/byethrow';
const
const result: Result.Result<never, "error">
result
=
import Result
Result
.
const pipe: <Result.Result<never, "error">, Result.Result<never, "error">>(a: Result.Result<never, "error">, ab: (a: Result.Result<never, "error">) => Result.Result<never, "error">) => Result.Result<never, "error"> (+25 overloads)
pipe
(
import Result
Result
.
const fail: <"error">(error: "error") => Result.Result<never, "error"> (+1 overload)
fail
('error'),
import Result
Result
.
const inspect: <Result.Result<never, "error">, void>(fn: (a: never) => void) => (result: Result.Result<never, "error">) => Result.Result<never, "error"> (+1 overload)
inspect
((
value: never
value
) =>
var console: 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
@seesource
console
.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)

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.

@sincev0 .1.100
log
('Value:',
value: never
value
)), // Not called
); // { type: 'Failure', error: 'error' }

inspectError - Peek at Error Values

inspectError is the counterpart for failure values:

import { 
import Result
Result
} from '@praha/byethrow';
const
const result: Result.Result<never, "Something went wrong">
result
=
import Result
Result
.
const pipe: <Result.Result<never, "Something went wrong">, Result.Result<never, "Something went wrong">>(a: Result.Result<never, "Something went wrong">, ab: (a: Result.Result<never, "Something went wrong">) => Result.Result<never, "Something went wrong">) => Result.Result<never, "Something went wrong"> (+25 overloads)
pipe
(
import Result
Result
.
const fail: <"Something went wrong">(error: "Something went wrong") => Result.Result<never, "Something went wrong"> (+1 overload)
fail
('Something went wrong'),
import Result
Result
.
const inspectError: <Result.Result<never, "Something went wrong">, void>(fn: (a: "Something went wrong") => void) => (result: Result.Result<never, "Something went wrong">) => Result.Result<never, "Something went wrong"> (+1 overload)
inspectError
((
error: "Something went wrong"
error
) =>
var console: 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
@seesource
console
.
Console.error(message?: any, ...optionalParams: any[]): void (+1 overload)

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.

@sincev0 .1.100
error
('Error:',
error: "Something went wrong"
error
)),
); // Console: "Error: Something went wrong" // { type: 'Failure', error: 'Something went wrong' }

On success, inspectError does nothing:

import { 
import Result
Result
} from '@praha/byethrow';
const
const result: Result.Result<42, never>
result
=
import Result
Result
.
const pipe: <Result.Result<42, never>, Result.Result<42, never>>(a: Result.Result<42, never>, ab: (a: Result.Result<42, never>) => Result.Result<42, never>) => Result.Result<42, never> (+25 overloads)
pipe
(
import Result
Result
.
const succeed: <42>(value: 42) => Result.Result<42, never> (+1 overload)
succeed
(42),
import Result
Result
.
const inspectError: <Result.Result<42, never>, void>(fn: (a: never) => void) => (result: Result.Result<42, never>) => Result.Result<42, never> (+1 overload)
inspectError
((
error: never
error
) =>
var console: 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
@seesource
console
.
Console.error(message?: any, ...optionalParams: any[]): void (+1 overload)

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.

@sincev0 .1.100
error
('Error:',
error: never
error
)), // Not called
); // { type: 'Success', value: 42 }

Example: Trace the Pipeline

import { 
import Result
Result
} from '@praha/byethrow';
const
const processData: (input: Input) => Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">
processData
= (
input: Input
input
:
type Input = {
    data: string;
}
Input
) => {
return
import Result
Result
.
const pipe: <Result.Result<Input, never>, Result.Result<Input, never>, Result.Result<Input, "ValidateFailed">, Result.Result<Input, "ValidateFailed">, Result.Result<Transformed, "ValidateFailed" | "TransformFailed">, Result.Result<Transformed, "ValidateFailed" | "TransformFailed">, Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">, Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">, Result.Result<...>>(a: Result.Result<...>, ab: (a: Result.Result<...>) => Result.Result<...>, bc: (b: Result.Result<...>) => Result.Result<...>, cd: (c: Result.Result<...>) => Result.Result<...>, de: (d: Result.Result<...>) => Result.Result<...>, ef: (e: Result.Result<...>) => Result.Result<...>, fg: (f: Result.Result<...>) => Result.Result<...>, gh: (g: Result.Result<...>) => Result.Result<...>, hi: (h: Result.Result<...>) => Result.Result<...>) => Result.Result<...> (+25 overloads)
pipe
(
import Result
Result
.
const succeed: <Input>(value: Input) => Result.Result<Input, never> (+1 overload)
succeed
(
input: Input
input
),
import Result
Result
.
const inspect: <Result.Result<Input, never>, void>(fn: (a: Input) => void) => (result: Result.Result<Input, never>) => Result.Result<Input, never> (+1 overload)
inspect
((
value: Input
value
) =>
var console: 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
@seesource
console
.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)

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.

@sincev0 .1.100
log
('Input:',
value: Input
value
)),
import Result
Result
.
const andThrough: <Result.Result<Input, never>, Result.Result<Input, "ValidateFailed">>(fn: (a: Input) => Result.Result<Input, "ValidateFailed">) => (result: Result.Result<Input, never>) => Result.Result<Input, "ValidateFailed"> (+1 overload)
andThrough
(
const validate: (input: Input) => Result.Result<Input, "ValidateFailed">
validate
),
import Result
Result
.
const inspect: <Result.Result<Input, "ValidateFailed">, void>(fn: (a: Input) => void) => (result: Result.Result<Input, "ValidateFailed">) => Result.Result<Input, "ValidateFailed"> (+1 overload)
inspect
((
value: Input
value
) =>
var console: 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
@seesource
console
.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)

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.

@sincev0 .1.100
log
('After validation:',
value: Input
value
)),
import Result
Result
.
const andThen: <Result.Result<Input, "ValidateFailed">, Result.Result<Transformed, "TransformFailed">>(fn: (a: Input) => Result.Result<Transformed, "TransformFailed">) => (result: Result.Result<Input, "ValidateFailed">) => Result.Result<Transformed, "ValidateFailed" | "TransformFailed"> (+1 overload)
andThen
(
const transform: (input: Input) => Result.Result<Transformed, "TransformFailed">
transform
),
import Result
Result
.
const inspect: <Result.Result<Transformed, "ValidateFailed" | "TransformFailed">, void>(fn: (a: Transformed) => void) => (result: Result.Result<Transformed, "ValidateFailed" | "TransformFailed">) => Result.Result<Transformed, "ValidateFailed" | "TransformFailed"> (+1 overload)
inspect
((
value: Transformed
value
) =>
var console: 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
@seesource
console
.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)

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.

@sincev0 .1.100
log
('After transform:',
value: Transformed
value
)),
import Result
Result
.
const andThen: <Result.Result<Transformed, "ValidateFailed" | "TransformFailed">, Result.Result<Saved, "SaveFailed">>(fn: (a: Transformed) => Result.Result<Saved, "SaveFailed">) => (result: Result.Result<Transformed, "ValidateFailed" | "TransformFailed">) => Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed"> (+1 overload)
andThen
(
const save: (input: Transformed) => Result.Result<Saved, "SaveFailed">
save
),
import Result
Result
.
const inspect: <Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">, void>(fn: (a: Saved) => void) => (result: Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">) => Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed"> (+1 overload)
inspect
((
value: Saved
value
) =>
var console: 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
@seesource
console
.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)

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.

@sincev0 .1.100
log
('After save:',
value: Saved
value
)),
import Result
Result
.
const inspectError: <Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">, void>(fn: (a: "ValidateFailed" | "TransformFailed" | "SaveFailed") => void) => (result: Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">) => Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed"> (+1 overload)
inspectError
((
error: "ValidateFailed" | "TransformFailed" | "SaveFailed"
error
) =>
var console: 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
@seesource
console
.
Console.error(message?: any, ...optionalParams: any[]): void (+1 overload)

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.

@sincev0 .1.100
error
('Pipeline failed:',
error: "ValidateFailed" | "TransformFailed" | "SaveFailed"
error
)),
); };

References

FunctionPurpose
inspect(fn)Run a side effect on the success value
inspectError(fn)Run a side effect on the error value