Never Nesting

Definition

The Never Nesting Pattern is a coding practice that eliminates deep nesting by using guard clauses and early returns. Instead of building confusing, nested if-else structures, you validate conditions early and exit the function immediately when conditions aren’t met.

Core Principle

“Fail fast, return home early!”

The Problem

Deep nesting is hard to understand and reduces code readability. The main logic gets buried under layers of conditional statements. Most developers simply call it ugly and say it burns their eyes.

Nested Nightmare

function processUser(user) {
    if (user) {
        if (user.isActive) {
            if (user.hasPermission) {
                if (user.email) {
                    // Finally, the actual logic
                    return sendEmail(user.email);
                } else {
                    throw new Error('No email');
                }
            } else {
                throw new Error('No permission');
            }
        } else {
            throw new Error('User inactive');
        }
    } else {
        throw new Error('User null');
    }
}

The Solution

Use guard clauses to handle edge cases first, then execute the main logic at the base indentation level.

Clean Implementation

function processUser(user) {
    if (!user) {
        throw new Error('User null');
    }
    
    if (!user.isActive) {
        throw new Error('User inactive');
    }
    
    if (!user.hasPermission) {
        throw new Error('No permission');
    }
    
    if (!user.email) {
        throw new Error('No email');
    }
    
    return sendEmail(user.email);
}

Real-World Example

API Endpoint Handler

async function handleUserRegistration(req, res) {
    if (!req.body.email) {
        return res.status(400).json({ error: 'Email required' });
    }
    
    if (!req.body.password) {
        return res.status(400).json({ error: 'Password required' });
    }
    
    if (req.body.password.length < 8) {
        return res.status(400).json({ error: 'Password too short' });
    }
    
    // Happy path - main registration logic
    const user = await createUser(req.body);
    res.status(201).json(user);
}