パターンマッチング

複数の異なるエラー型を持つ Result 型を扱う際、異なるエラーシナリオを効果的に処理するためにパターンマッチングは不可欠です。 このガイドでは、複数のエラー型を適切に処理するためのパターンマッチングの使い方を示します。

なぜユニオンエラーにパターンマッチングが必要なのか?

Result が複数の異なるエラー型で失敗する可能性がある場合、各エラー型を適切に処理する体系的な方法が必要です。 パターンマッチングは、すべての可能なエラーケースを処理するためのクリーンで型安全なアプローチを提供します。

Tip

@praha/error-factory の詳細については、Custom Errorページを参照してください。

import { 
const ErrorFactory: {
    <Name extends string, Message extends string, Fields extends ErrorFields>(props: {
        name: Name;
        message: Message | ((fields: Fields) => Message);
        fields?: Fields;
    }): ErrorConstructor<Name, Message, Fields>;
    fields<Fields extends ErrorFields>(): Fields;
}
ErrorFactory
} from '@praha/error-factory';
import {
import Result
Result
} from '@praha/byethrow';
class
class PostNotFoundError
PostNotFoundError
extends
ErrorFactory<"PostNotFoundError", "The requested post was not found.", ErrorFields>(props: {
    name: "PostNotFoundError";
    message: "The requested post was not found." | ((fields: ErrorFields) => "The requested post was not found.");
    fields?: ErrorFields | undefined;
}): (new (options?: ErrorOptions) => Error & Readonly<{
    name: "PostNotFoundError";
    message: "The requested post was not found.";
}>) & {
    name: "PostNotFoundError";
}
ErrorFactory
({
name: "PostNotFoundError"
name
: 'PostNotFoundError',
message: "The requested post was not found." | ((fields: ErrorFields) => "The requested post was not found.")
message
: 'The requested post was not found.',
}) {} class
class PostPermissionError
PostPermissionError
extends
ErrorFactory<"PostPermissionError", "You do not have permission to perform this action.", ErrorFields>(props: {
    name: "PostPermissionError";
    message: "You do not have permission to perform this action." | ((fields: ErrorFields) => "You do not have permission to perform this action.");
    fields?: ErrorFields | undefined;
}): (new (options?: ErrorOptions) => Error & Readonly<{
    name: "PostPermissionError";
    message: "You do not have permission to perform this action.";
}>) & {
    name: "PostPermissionError";
}
ErrorFactory
({
name: "PostPermissionError"
name
: 'PostPermissionError',
message: "You do not have permission to perform this action." | ((fields: ErrorFields) => "You do not have permission to perform this action.")
message
: 'You do not have permission to perform this action.',
}) {} class
class PostAlreadyDeletedError
PostAlreadyDeletedError
extends
ErrorFactory<"PostAlreadyDeletedError", "This post has already been deleted.", ErrorFields>(props: {
    name: "PostAlreadyDeletedError";
    message: "This post has already been deleted." | ((fields: ErrorFields) => "This post has already been deleted.");
    fields?: ErrorFields | undefined;
}): (new (options?: ErrorOptions) => Error & Readonly<{
    name: "PostAlreadyDeletedError";
    message: "This post has already been deleted.";
}>) & {
    name: "PostAlreadyDeletedError";
}
ErrorFactory
({
name: "PostAlreadyDeletedError"
name
: 'PostAlreadyDeletedError',
message: "This post has already been deleted." | ((fields: ErrorFields) => "This post has already been deleted.")
message
: 'This post has already been deleted.',
}) {} // 投稿削除関数の例 type
type PostDeleteError = PostNotFoundError | PostPermissionError | PostAlreadyDeletedError
PostDeleteError
= (
|
class PostNotFoundError
PostNotFoundError
|
class PostPermissionError
PostPermissionError
|
class PostAlreadyDeletedError
PostAlreadyDeletedError
); // 複数のエラー型を返す可能性がある関数 const
const deletePost: (postId: string) => Result.ResultAsync<void, PostDeleteError>
deletePost
= async (
postId: string
postId
: string):
import Result
Result
.
type ResultAsync<T, E> = Promise<Result.Result<T, E>>

An asynchronous variant of Result , wrapped in a Promise.

@typeParamT - The type of the Success value.@typeParamE - The type of the Failure value.@example
import { Result } from '@praha/byethrow';

const fetchData = async (): Result.ResultAsync<string, Error> => {
  try {
    const data = await fetch('...');
    return { type: 'Success', value: await data.text() };
  } catch (err) {
    return { type: 'Failure', error: err as Error };
  }
};
@categoryCore Types
ResultAsync
<void,
type PostDeleteError = PostNotFoundError | PostPermissionError | PostAlreadyDeletedError
PostDeleteError
> => {
// いずれかのエラー型を返す可能性のある実装 }; // パターンマッチングによる結果のハンドリング await
import Result
Result
.
const pipe: <Result.ResultAsync<void, PostDeleteError>, Result.ResultAsync<string, PostDeleteError>, Result.ResultAsync<string, PostDeleteError>>(a: Result.ResultAsync<void, PostDeleteError>, ab: (a: Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<string, PostDeleteError>, bc: (b: Result.ResultAsync<string, PostDeleteError>) => Result.ResultAsync<string, PostDeleteError>) => Result.ResultAsync<...> (+25 overloads)
pipe
(
const deletePost: (postId: string) => Result.ResultAsync<void, PostDeleteError>
deletePost
('123'),
import Result
Result
.
const map: <Result.ResultAsync<void, PostDeleteError>, string>(fn: (a: void) => string) => (result: Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<string, PostDeleteError> (+1 overload)
map
(() => 'Post deleted successfully!'),
import Result
Result
.
const inspectError: <Result.ResultAsync<string, PostDeleteError>, void>(fn: (a: PostDeleteError) => void) => (result: Result.ResultAsync<string, PostDeleteError>) => Result.ResultAsync<string, PostDeleteError> (+1 overload)
inspectError
((
error: PostDeleteError
error
) => {
// 異なるエラー型を処理するためのパターンマッチング }), );

推奨:ts-pattern を使用する

パターンマッチングにはts-patternの使用を強くお勧めします。 優れたTypeScriptサポートを提供し、網羅的なマッチングを保証します。

インストール

npm
yarn
pnpm
bun
deno
npm install ts-pattern

ts-pattern によるパターンマッチング

import { 
import Result
Result
} from '@praha/byethrow';
import {
function match<const input, output = typeof unset>(value: input): Match<input, output>

match creates a pattern matching expression.

  • Use .with(pattern, handler) to pattern match on the input.
  • Use .exhaustive() or .otherwise(() => defaultValue) to end the expression and get the result.

Read the documentation for match on GitHub

@example

declare let input: "A" | "B";

return match(input) .with("A", () => "It's an A!") .with("B", () => "It's a B!") .exhaustive();

match
} from 'ts-pattern';
await
import Result
Result
.
const pipe: <Result.ResultAsync<void, PostDeleteError>, Result.ResultAsync<void, PostDeleteError>>(a: Result.ResultAsync<void, PostDeleteError>, ab: (a: Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<void, PostDeleteError> (+25 overloads)
pipe
(
function deletePost(postId: string): Result.ResultAsync<void, PostDeleteError>
deletePost
('123'),
import Result
Result
.
const inspectError: <Result.ResultAsync<void, PostDeleteError>, void>(fn: (a: PostDeleteError) => void) => (result: Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<void, PostDeleteError> (+1 overload)
inspectError
((
error: PostDeleteError
error
) => {
match<PostDeleteError, typeof unset>(value: PostDeleteError): Match<PostDeleteError, typeof unset>

match creates a pattern matching expression.

  • Use .with(pattern, handler) to pattern match on the input.
  • Use .exhaustive() or .otherwise(() => defaultValue) to end the expression and get the result.

Read the documentation for match on GitHub

@example

declare let input: "A" | "B";

return match(input) .with("A", () => "It's an A!") .with("B", () => "It's a B!") .exhaustive();

match
(
error: PostDeleteError
error
)
.
with<{
    readonly name: "PostNotFoundError";
}, void, PostNotFoundError>(pattern: {
    readonly name: "PostNotFoundError";
}, handler: (selections: PostNotFoundError, value: PostNotFoundError) => void): Match<PostPermissionError | PostAlreadyDeletedError, typeof unset, [{
    readonly name: "PostNotFoundError";
}], void> (+3 overloads)

.with(pattern, handler) Registers a pattern and an handler function that will be called if the pattern matches the input value.

Read the documentation for .with() on GitHub

with
({
name: "PostNotFoundError"
name
: 'PostNotFoundError' }, () => {
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
('リクエストされた投稿が見つかりませんでした。');
}) .
with<{
    readonly name: "PostPermissionError";
}, void, PostPermissionError>(pattern: {
    readonly name: "PostPermissionError";
}, handler: (selections: PostPermissionError, value: PostPermissionError) => void): Match<PostAlreadyDeletedError, typeof unset, [{
    readonly name: "PostNotFoundError";
}, {
    readonly name: "PostPermissionError";
}], void> (+3 overloads)

.with(pattern, handler) Registers a pattern and an handler function that will be called if the pattern matches the input value.

Read the documentation for .with() on GitHub

with
({
name: "PostPermissionError"
name
: 'PostPermissionError' }, () => {
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
('このアクションを実行する権限がありません。');
}) .
with<{
    readonly name: "PostAlreadyDeletedError";
}, void, PostAlreadyDeletedError>(pattern: {
    readonly name: "PostAlreadyDeletedError";
}, handler: (selections: PostAlreadyDeletedError, value: PostAlreadyDeletedError) => void): Match<never, typeof unset, [{
    readonly name: "PostNotFoundError";
}, {
    readonly name: "PostPermissionError";
}, {
    readonly name: "PostAlreadyDeletedError";
}], void> (+3 overloads)

.with(pattern, handler) Registers a pattern and an handler function that will be called if the pattern matches the input value.

Read the documentation for .with() on GitHub

with
({
name: "PostAlreadyDeletedError"
name
: 'PostAlreadyDeletedError' }, () => {
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
('この投稿は既に削除されています。');
}) .
exhaustive: () => void (+1 overload)

.exhaustive() checks that all cases are handled, and returns the result value.

If you get a NonExhaustiveError, it means that you aren't handling all cases. You should probably add another .with(...) clause to match the missing case and prevent runtime errors.

Read the documentation for .exhaustive() on GitHub

exhaustive
(); // すべてのケースが処理されることを保証する
}), );

代替案:TypeScriptネイティブなパターンマッチング

外部ライブラリを使用したくない場合は、TypeScriptの組み込み機能を使用してパターンマッチングを実装できます。

instanceof を使用する

import { 
import Result
Result
} from '@praha/byethrow';
await
import Result
Result
.
const pipe: <Result.ResultAsync<void, PostDeleteError>, Result.ResultAsync<void, PostDeleteError>>(a: Result.ResultAsync<void, PostDeleteError>, ab: (a: Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<void, PostDeleteError> (+25 overloads)
pipe
(
function deletePost(postId: string): Result.ResultAsync<void, PostDeleteError>
deletePost
('123'),
import Result
Result
.
const inspectError: <Result.ResultAsync<void, PostDeleteError>, void>(fn: (a: PostDeleteError) => void) => (result: Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<void, PostDeleteError> (+1 overload)
inspectError
((
error: PostDeleteError
error
) => {
if (
error: PostDeleteError
error
instanceof
class PostNotFoundError
PostNotFoundError
) {
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
('リクエストされた投稿が見つかりませんでした。');
} if (
error: PostDeleteError
error
instanceof
class PostPermissionError
PostPermissionError
) {
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
('このアクションを実行する権限がありません。');
} if (
error: PostDeleteError
error
instanceof
class PostAlreadyDeletedError
PostAlreadyDeletedError
) {
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
('この投稿は既に削除されています。');
} }), );

判別可能なユニオンを使用する

import { 
import Result
Result
} from '@praha/byethrow';
await
import Result
Result
.
const pipe: <Result.ResultAsync<void, PostDeleteError>, Result.ResultAsync<void, PostDeleteError>>(a: Result.ResultAsync<void, PostDeleteError>, ab: (a: Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<void, PostDeleteError> (+25 overloads)
pipe
(
function deletePost(postId: string): Result.ResultAsync<void, PostDeleteError>
deletePost
('123'),
import Result
Result
.
const inspectError: <Result.ResultAsync<void, PostDeleteError>, void>(fn: (a: PostDeleteError) => void) => (result: Result.ResultAsync<void, PostDeleteError>) => Result.ResultAsync<void, PostDeleteError> (+1 overload)
inspectError
((
error: PostDeleteError
error
) => {
switch (
error: PostDeleteError
error
.
Error.name: "PostNotFoundError" | "PostPermissionError" | "PostAlreadyDeletedError"
name
) {
case 'PostNotFoundError':
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
('リクエストされた投稿が見つかりませんでした。');
break; case 'PostPermissionError':
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
('このアクションを実行する権限がありません。');
break; case 'PostAlreadyDeletedError':
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
('この投稿は既に削除されています。');
break; default: // すべてのエラー型がカバーされていれば、ここには到達しないはず const
const _exhaustiveCheck: never
_exhaustiveCheck
: never =
error: never
error
;
throw new
var Error: ErrorConstructor
new (message?: string, options?: ErrorOptions) => Error (+1 overload)
Error
(`Unhandled error type: ${
var JSON: JSON

An intrinsic object that provides functions to convert JavaScript values to and from the JavaScript Object Notation (JSON) format.

JSON
.
JSON.stringify(value: any, replacer?: (this: any, key: string, value: any) => any, space?: string | number): string (+1 overload)

Converts a JavaScript value to a JavaScript Object Notation (JSON) string.

@paramvalue A JavaScript value, usually an object or array, to be converted.@paramreplacer A function that transforms the results.@paramspace Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.@throws{TypeError} If a circular reference or a BigInt value is found.
stringify
(
const _exhaustiveCheck: never
_exhaustiveCheck
)}`);
} }), );