paralleldrive/aidd/aidd-error-causes

Claude Code and agent skill by paralleldrive/aidd

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Use the error-causes library for structured error handling in JavaScript/TypeScript. Use when throwing errors, catching errors, defining error types, or implementing error routing.

Install

npx vskill@latest install paralleldrive/aidd/aidd-error-causes

SKILL.md

Error Causes Rule

Use the error-causes library for all error handling in JavaScript/TypeScript code to enable structured error handling with named causes.

Why Error Causes?

  • Enables structured error handling with named causes instead of relying on instanceof checks
  • Works across memory realms (e.g., iframes) unlike instanceof
  • Provides consistent error metadata (name, code, message, cause)
  • Makes error handling explicit and self-documenting
  • Allows for automatic error routing based on error names

Import Statement

js
import { createError } from "error-causes";

Basic Usage

Instead of throwing plain errors:

js
// ❌ DON'T
throw new Error('Config key "API_KEY" is required');

Use createError with structured metadata:

js
// ✅ DO
throw createError({
  name: 'ConfigurationError',
  message: 'Required configuration key "API_KEY" is not defined',
  code: 'MISSING_CONFIG_KEY',
  requestedKey: 'API_KEY'
});

Error Properties

Always include these properties in createError:

  • name - Error name for matching (e.g., 'ValidationError', 'AuthenticationError')
  • message - Human-readable error message
  • code (optional) - Error code for programmatic handling
  • Custom properties (optional) - Any additional context relevant to the error

Wrapping Caught Errors

When catching and re-throwing errors, preserve the original error as cause:

js
try {
  await someOperation();
} catch (originalError) {
  throw createError({
    name: 'OperationError',
    message: 'Failed to perform operation',
    code: 'OPERATION_FAILED',
    cause: originalError  // Preserve original error
  });
}

Factory Validation Errors

For factory functions that validate parameters at creation time:

js
const createMiddleware = ({ requiredParam } = {}) => {
  if (!requiredParam) {
    throw createError({
      name: 'ValidationError',
      message: 'requiredParam is required',
      code: 'MISSING_REQUIRED_PARAM'
    });
  }
  return async ({ request, response }) => {
    // middleware implementation
  };
};

Testing Error Causes

In tests, verify the error's cause property:

js
let error;
try {
  functionThatThrows();
} catch (e) {
  error = e;
}
assert({
  given: 'invalid input',
  should: 'throw Error with cause',
  actual: error instanceof Error && error.cause !== undefined,
  expected: true
});
assert({
  given: 'invalid input',
  should: 'have correct error name',
  actual: error.cause.name,
  expected: 'ValidationError'
});
assert({
  given: 'invalid input',
  should: 'have correct error code',
  actual: error.cause.code,
  expected: 'MISSING_REQUIRED_PARAM'
});

Error Handler Pattern

For APIs that define multiple error types, use the errorCauses pattern:

js
import { errorCauses, createError } from "error-causes";
// Define all possible errors for your API
const [apiErrors, handleApiErrors] = errorCauses({
  NotFound: {
    code: 404,
    message: 'Resource not found'
  },
  ValidationError: {
    code: 400,
    message: 'Invalid input'
  },
  Unauthorized: {
    code: 401,
    message: 'Authentication required'
  }
});
const { NotFound, ValidationError, Unauthorized } = apiErrors;
// Throw errors
if (!resource) throw createError(NotFound);
// Handle errors with automatic routing
someAsyncCall()
  .catch(handleApiErrors({
    NotFound: ({ message }) => console.log(message),
    ValidationError: ({ message }) => console.log(message),
    Unauthorized: ({ message }) => redirect('/login')
  }));

Rules

  1. Always use `createError` instead of new Error() for thrown errors
  2. Always include `name` and `message` in error metadata
  3. Include `code` when the error needs programmatic handling
  4. Preserve original errors using the cause property when re-throwing
  5. Add context with custom properties relevant to the error
  6. Test the `cause` property in error tests, not just the error message
  7. Define error types using errorCauses() for APIs with multiple error types

Security

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  • Model reviewPassed

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Source

Popularity

Repository stars
383
Repository forks
33
Repository npm downloads, 7 days
945
7-day trend score
46

Stars and forks are for the whole GitHub repository, not this skill alone. Downloads are for the repository's npm package. Refreshed 29 Apr 2026, 6 months ago.

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