causality-error

Go-like errors.Is utility for JavaScript/TypeScript.

Installation

# npm
npm install causality-error

# yarn
yarn add causality-error

# pnpm
pnpm add causality-error

Usage

import { is } from 'causality-error';

// Example 1: Check if an error is an instance of a specific constructor
try {
  JSON.parse('invalid json');
} catch (err) {
  if (is(err, SyntaxError)) {
    console.log('Caught a SyntaxError');
  }
}

// Example 2: Check for a specific error instance
const specificError = new Error('specific error');
const wrappedError = new Error('wrapper', { cause: specificError });

if (is(wrappedError, specificError)) {
  console.log('Found the specific error in the cause chain');
}

// Example 3: Check using a predicate function
const fsError = Object.assign(new Error('file not found'), { code: 'ENOENT' });
const wrappedFsError = new Error('operation failed', { cause: fsError });

if (is(wrappedFsError, e => (e as any).code === 'ENOENT')) {
  console.log('Found a file not found error');
}

// Example 4: Works with AggregateError
const aggregateError = new AggregateError(
  [new TypeError('bad type'), new RangeError('bad range')],
  'multiple errors'
);

if (is(aggregateError, RangeError)) {
  console.log('Found a RangeError in the aggregate error');
}

API

is(err, target)

Checks if err matches target anywhere in its cause chain.

Parameters

• err: unknown - The error to check
• target: unknown | ErrorCtor | ErrorPredicate - The target to match against, which can be:
  • An error instance (checks for exact match)
  • An error constructor (checks using instanceof)
  • A predicate function (checks using the function)

Returns

• boolean - true if the error matches the target, false otherwise

License

MIT