reduce-optional-params（减少可选参数）

Reduce Optional Parameters

Guidance for simplifying function and component signatures by reducing optional parameters. Too many optional params make call sites hard to read and APIs fragile.

When to Apply

• Designing new functions or components
• Refactoring code with many optional arguments
• Code review when spotting 3+ optional params
• User asks about cleaner API design or reducing optional params

Before adding an optional param, ask: (1) Is there a concrete use case? (2) Would a separate function or preset make intent clearer? (3) Would callers pass this only in a few places? (If yes, a dedicated function or preset may be clearer.)

Strategies (Choose by Context)

1. Options Object

Group related optional params into a single config object.

// Before
function fetchUser(id: string, includeProfile?: boolean, cache?: boolean, timeout?: number) {}

// After
function fetchUser(id: string, options?: { includeProfile?: boolean; cache?: boolean; timeout?: number }) {}

Use when: Params are loosely related and callers typically pass 0–2 at a time.

Edge case: If one option is required in most call sites, keep it as a required positional param and put the rest in the options object (e.g. fetchUser(id, {includeProfile: true})).

2. Split Into Focused Functions

Replace one function with many optional params with smaller, purpose-specific functions.

// Before
function createButton(text: string, variant?: string, size?: string, disabled?: boolean, icon?: string) {}

// After
function createPrimaryButton(text: string, opts?: { size?: string }) {}
function createIconButton(text: string, icon: string, opts?: { size?: string }) {}

Use when: Optional params create distinct usage modes (e.g. "icon mode" vs "text-only").

3. Composition (React/Components)

Use children, compound components, or render props instead of optional props.

// Before
<Button text="Save" variant="primary" size="md" leftIcon={<SaveIcon />} rightIcon={null} loading={false} />

// After
<Button variant="primary" size="md">
  <Button.Icon><SaveIcon /></Button.Icon>
  Save
</Button>

Use when: UI has many configurable facets that rarely combine.

4. Factory or Preset Functions

Expose presets for common configurations instead of one function with many options.

// Before
function connect(url: string, retries?: number, timeout?: number, ssl?: boolean) {}

// After
function connect(url: string, opts?: ConnectionOptions) {}
function connectProduction(url: string) {
  return connect(url, { retries: 3, timeout: 5000, ssl: true });
}

Use when: A few well-defined configurations dominate usage.

5. Narrower Required Params

Move "optional" params into a narrower function where they become required.

// Before
function render(component: Component, layout?: string, theme?: string) {}

// After
function render(component: Component) {}
function renderWithLayout(component: Component, layout: string, theme?: string) {}

Use when: Some params are optional only in the generic path but required in specific paths.

6. Builder Pattern (When Fluent API Fits)

Use a builder when callers need to set many options and discoverability helps.

// Before
createModal(title: string, content: string, closable?: boolean, width?: number, onClose?: () => void) {}

// After
Modal.create(title, content).closable(true).width(400).onClose(handler).show()

Use when: 5+ options and fluent-style API is acceptable in the codebase.

Decision Flow

1. 2–3 optional params → Options object
2. Distinct usage modes → Split into focused functions
3. UI/component → Prefer composition over many optional props
4. Common presets → Factory/preset functions
5. Generic vs specific paths → Narrower functions with required params
6. 5+ options, complex config → Builder or options object
7. None of the above fits → Prefer options object to keep one function; document defaults and avoid optional params that change behavior in non-obvious ways.

Anti-Patterns

• Don’t add optional params "for flexibility" without concrete use cases
• Avoid optional params that change behavior in non-obvious ways (use separate functions)
• Don’t mix positional optional params with an options object