clean-code-functions

Clean Code: Function Structure

Method Parameter Design

Avoid Boolean Parameters

Boolean parameters hide intent at the call site. The reader cannot understand what true means without looking at the method signature.

// BAD - What does 'true' mean?
processOrder(order, true)
saveUser(user, false, true)

// GOOD - Intent is clear from method name
processOrder(order)
processOrderWithNotification(order)

saveUser(user)
saveUserWithValidation(user)

Exception: Boolean parameters are acceptable when the method name makes the meaning obvious (e.g., setVisible(true)).

Limit Parameter Count

• Ideal: 0-3 parameters
• Acceptable: 4 parameters with clear purpose
• Refactor: 5+ parameters — use a parameter object or builder pattern

// BAD - Too many parameters, easy to mix up
createUser(name, email, age, department, role, isActive, sendWelcome)

// GOOD - Parameter object groups related data
createUser(CreateUserRequest request)

Single Level of Abstraction

Each function should operate at one level of abstraction. Don't mix high-level orchestration with low-level details.

// BAD - Mixed abstraction levels
function processOrder(order) {
    validateOrder(order)                           // High-level
    const tax = order.subtotal * 0.0825            // Low-level detail
    sendToFulfillment(order)                        // High-level
    db.query("INSERT INTO audit_log...")           // Low-level detail
}

// GOOD - Consistent abstraction level
function processOrder(order) {
    validateOrder(order)
    calculateTotals(order)
    sendToFulfillment(order)
    logOrderProcessed(order)
}

Keep Functions Short

• Aim for ~20 lines (fits on one screen)
• If a function requires scrolling, consider extracting parts
• Each function should do one thing well

Guard Clauses First

Validate inputs and handle edge cases at the top of the function. Return early to avoid deep nesting.

// BAD - Deep nesting
function getDiscount(user) {
    if (user != null) {
        if (user.isActive) {
            if (user.membershipYears > 5) {
                return 0.20
            }
        }
    }
    return 0
}

// GOOD - Guard clauses with early returns
function getDiscount(user) {
    if (user == null) return 0
    if (!user.isActive) return 0
    if (user.membershipYears <= 5) return 0
    
    return 0.20
}