@studnicky/require-options-object

When a function or method has two or more caller-omittable parameter slots, they must be collected into a single trailing options object. The threshold defaults to minimumOptionals: 2 and is configurable. The rule counts ? parameters, defaulted parameters, parameters typed T | undefined, and optional members of a rest tuple. It applies to function declarations, function expressions, arrow functions, and TypeScript call, construct, function, and method signatures.

Fixable: No · Options: minimumOptionals · Suggested severity: error

Detection

A parameter whose own type annotation is a union that includes undefined (value: T | undefined) counts as one optional slot even without a ? or a default value, since a caller may pass undefined explicitly at any call site. A rest parameter typed as a tuple (...args: [name?: string, age?: number]) is not a single non-optional unit: each optional tuple member contributes its own optional slot to the count — a named tuple member marks itself via optional: true, and an unnamed member wraps its element type in TSOptionalType.

A trailing parameter satisfies the options-object requirement only when its type literal declares at least one named member (a property or method signature). An empty {} or a pure index-signature literal ({ [key: string]: unknown }) carries none of a real options object's type safety, so neither is accepted as the collecting parameter.

✗ Incorrect

// Two optional parameters — collect into options object
function fetch(url: string, timeout?: number, retries?: number): Promise<Response> {
  /* ... */
}

// Three optional parameters on a method
class HttpClient {
  request(url: string, method?: string, body?: string, signal?: AbortSignal): Promise<Response> {
    /* ... */
  }
}

✓ Correct

// Collected into a trailing options object
function fetch(url: string, opts?: { timeout?: number; retries?: number }): Promise<Response> {
  /* ... */
}

// Method with options object
class HttpClient {
  request(url: string, opts?: { method?: string; body?: string; signal?: AbortSignal }): Promise<Response> {
    /* ... */
  }
}

Options

{
  "@studnicky/require-options-object": ["error", { "minimumOptionals": 2 }]
}

Option	Type	Default	Description
minimumOptionals	integer	2	Minimum number of caller-omittable parameter slots before an options object is required. Minimum value is 2.