Brain Method

Function Strategy  |  Multi-metric

A function that has become the cognitive centre of a component — too long to skim, too complex to reason about, and too deeply nested to modify safely.

Detection Rule

Note: The nesting metric here uses max_nesting (maximum control-flow depth), and the length uses SLOC (source lines of code — blank lines and comments excluded), not raw LOC.

TypeScript Example

function processPayment(req: PaymentRequest): PaymentResult {
  // 80 SLOC, CC=9, max_nesting=5 → Brain Method
  if (req.type === "card") {
    for (const item of req.items) {
      if (item.taxable) {
        if (item.country === "US") {
          if (item.state === "CA") {
            // depth 5 ← exceeds threshold
          }
        }
      }
    }
  }
  // ... 60 more lines
}

Remediation

• Extract Method — pull inner blocks (especially inside deep nesting) into well-named helper functions.
• Replace conditional with polymorphism — large if/else trees often indicate missing dispatch.
• Early return / guard clauses — invert conditions to reduce nesting depth quickly.
• Aim for each function to fit on a single screen (< 40 SLOC) with CC ≤ 5.

Related strategies

God Class · Feature Envy

Related metrics

Cyclomatic Complexity · Maintainability Index · Technical Debt