single-or-array-pattern
Pattern for functions that accept either a single item or an array. Use when creating CRUD operations, batch processing APIs, or factory functions that should flexibly handle one or many inputs.
Installation
Details
Usage
After installing, this skill will be available to your AI coding assistant.
Verify installation:
skills listSkill Instructions
name: single-or-array-pattern description: Pattern for functions that accept either a single item or an array. Use when creating CRUD operations, batch processing APIs, or factory functions that should flexibly handle one or many inputs. metadata: author: epicenter version: '1.0'
Single-or-Array Overload Pattern
Accept both single items and arrays, normalize internally, delegate to array-only implementation.
Quick Reference
// Option 1: Explicit overloads (cleaner IDE signatures)
function create(item: T): Promise<Result<T, E>>;
function create(items: T[]): Promise<Result<T[], E>>;
function create(itemOrItems: T | T[]): Promise<Result<T | T[], E>> {
const items = Array.isArray(itemOrItems) ? itemOrItems : [itemOrItems];
return createInternal(items);
}
// Option 2: Union type (less boilerplate)
function create(itemOrItems: T | T[]): Promise<Result<void, E>> {
const items = Array.isArray(itemOrItems) ? itemOrItems : [itemOrItems];
// ... implementation
}
The Structure
- Public API: Accepts
T | T[] - Normalization:
Array.isArray()check, wrap single in array - Internal function: Only handles arrays
// Public: flexible API
function createServer(clientOrClients: Client | Client[], options?: Options) {
const clients = Array.isArray(clientOrClients)
? clientOrClients
: [clientOrClients];
return createServerInternal(clients, options);
}
// Internal: array-only, all real logic here
function createServerInternal(clients: Client[], options?: Options) {
// Implementation only handles arrays
}
Naming Conventions
| Parameter | Normalized Variable |
|---|---|
recordingOrRecordings | recordings |
clientOrClients | clients |
itemOrItems | items |
paramsOrParamsArray | paramsArray |
When to Use
Good fit:
- CRUD operations (create, update, delete)
- Batch processing APIs
- Factory functions accepting dependencies
- Any "do this to one or many" scenario
Skip when:
- Single vs batch have different semantics
- Return types vary significantly
- Array version needs different options
Codebase Examples
Server Factory (packages/epicenter/src/server/server.ts)
function createServer(
client: AnyWorkspaceClient,
options?: ServerOptions,
): ReturnType<typeof createServerInternal>;
function createServer(
clients: AnyWorkspaceClient[],
options?: ServerOptions,
): ReturnType<typeof createServerInternal>;
function createServer(
clientOrClients: AnyWorkspaceClient | AnyWorkspaceClient[],
options?: ServerOptions,
) {
const clients = Array.isArray(clientOrClients)
? clientOrClients
: [clientOrClients];
return createServerInternal(clients, options);
}
Database Service (apps/whispering/src/lib/services/isomorphic/db/web.ts)
delete: async (recordingOrRecordings) => {
const recordings = Array.isArray(recordingOrRecordings)
? recordingOrRecordings
: [recordingOrRecordings];
const ids = recordings.map((r) => r.id);
return tryAsync({
try: () => db.recordings.bulkDelete(ids),
catch: (error) => DbServiceErr({ message: `Error deleting: ${error}` }),
});
},
Query Mutations (apps/whispering/src/lib/query/isomorphic/db.ts)
delete: defineMutation({
mutationFn: async (recordings: Recording | Recording[]) => {
const recordingsArray = Array.isArray(recordings)
? recordings
: [recordings];
for (const recording of recordingsArray) {
services.db.recordings.revokeAudioUrl(recording.id);
}
const { error } = await services.db.recordings.delete(recordingsArray);
if (error) return Err(error);
return Ok(undefined);
},
}),
Anti-Patterns
Don't: Separate functions for single vs array
// Harder to maintain, users must remember two APIs
function createRecording(recording: Recording): Promise<...>;
function createRecordings(recordings: Recording[]): Promise<...>;
Don't: Force arrays everywhere
// Awkward for single items
createRecordings([recording]); // Ugly
Don't: Duplicate logic in overloads
// BAD: Logic duplicated
function create(item: T) {
return db.insert(item); // Duplicated
}
function create(items: T[]) {
return db.bulkInsert(items); // Different code path
}
// GOOD: Single implementation
function create(itemOrItems: T | T[]) {
const items = Array.isArray(itemOrItems) ? itemOrItems : [itemOrItems];
return db.bulkInsert(items); // One code path
}
References
- Full article — detailed explanation with more examples
More by EpicenterHQ
View allApply factory function patterns to compose clients and services with proper separation of concerns. Use when creating functions that depend on external clients, wrapping resources with domain-specific methods, or refactoring code that mixes client/service/method options together.
Git commit and pull request guidelines using conventional commits. Use when creating commits, writing commit messages, creating PRs, or reviewing PR descriptions.
Monorepo script commands and conventions for this codebase. Use when running builds, tests, formatting, linting, or type checking.
Behavioral guideline for providing brutally honest feedback. Use always - this skill defines core interaction expectations for code review and technical discussions.