code-complexity

Code Complexity

Limits at a Glance

Metric	Limit	Action When Exceeded
Cyclomatic complexity	< 15 per function	Extract helper functions
Function length	~50 lines max	Split into focused functions
File length	~300 lines max	Extract modules/classes
Nesting depth	Max 4 levels	Early returns, extract functions
Parameter count	Max 4-5 params	Use an options/config object
Duplicate blocks	> 3 lines repeated 2+ times	Extract shared function

Cyclomatic Complexity (< 15 per function)

Each if, else, case, &&, ||, catch, and ternary adds 1. When a function exceeds 15, extract validation, branching logic, or case handling into separate functions.

Function Length (~50 Lines Max)

If you need a comment like // Step 3: ..., that step is its own function.

// BAD -- 120-line function with section comments
function handleRequest(req: Request) { /* validate, fetch, transform, respond */ }

// GOOD -- each concern is a named function
function handleRequest(req: Request) {
  const input = validateInput(req);
  const data = fetchDependencies(input);
  return saveAndRespond(transformData(data));
}

Deep Nesting (Max 4 Levels)

// BAD -- 5 levels deep
function process(items) {
  if (items) {
    for (const item of items) {
      if (item.active) {
        if (item.type === 'premium') {
          if (item.balance > 0) { /* buried logic */ }
        }
      }
    }
  }
}

// GOOD -- flat with early returns and filtering
function process(items) {
  if (!items) return;
  const eligible = items.filter(i => i.active && i.type === 'premium' && i.balance > 0);
  for (const item of eligible) { /* top-level logic */ }
}

Parameter Count (Max 4-5)

// BAD -- 7 positional params
function createUser(name, email, role, team, avatar, locale, timezone) { ... }

// GOOD -- options object
interface CreateUserOptions {
  name: string; email: string; role: Role;
  team?: string; avatar?: string; locale?: string; timezone?: string;
}
function createUser(options: CreateUserOptions) { ... }