/engineering

name: engineering-fundamentals
description: Background knowledge for code quality. Applied when reviewing naming conventions, DRY, SOLID, function size, refactoring, or when junior asks "is this clean", "code review", "better way".
user-invocable: false

Engineering Fundamentals Review

> "Code is read more than it is written. Write for the reader, not the machine."

When to Apply

Activate this skill when reviewing:

• Any code changes
• Function and variable naming
• Code organization and structure
• General refactoring decisions

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Review Checklist

Naming

• [ ] **Descriptive**: Can you understand the variable without context?
• [ ] **No abbreviations**: Are names spelled out? (`user` not `usr`)
• [ ] **No generic names**: No `data`, `temp`, `info`, `stuff`?
• [ ] **Boolean prefix**: Do booleans start with `is`, `has`, `can`, `should`?
• [ ] **Function verbs**: Do functions start with action verbs?

Function Design

• [ ] **Single responsibility**: Does each function do ONE thing?
• [ ] **Size limit**: Are functions under 20-30 lines?
• [ ] **Parameter count**: Are there fewer than 4 parameters?
• [ ] **No side effects**: Are pure functions actually pure?
• [ ] **Early returns**: Are guard clauses used instead of deep nesting?

Code Organization

• [ ] **DRY**: Is duplicated code extracted into functions?
• [ ] **But not too DRY**: Are abstractions justified (rule of three)?
• [ ] **Cohesion**: Are related things grouped together?
• [ ] **Separation**: Are unrelated things separated?

Comments & Documentation

• [ ] **Why, not what**: Do comments explain reasoning, not obvious code?
• [ ] **No commented-out code**: Is dead code deleted, not commented?
• [ ] **JSDoc on public APIs**: Are exported functions documented?

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Common Mistakes (Anti-Patterns)

1. Magic Numbers

❌ if (status === 2) { ... }
   setTimeout(callback, 86400000);

✅ const STATUS = { ACTIVE: 2, INACTIVE: 1 };
   if (status === STATUS.ACTIVE) { ... }

   const ONE_DAY_MS = 24 * 60 * 60 * 1000;
   setTimeout(callback, ONE_DAY_MS);

2. Unclear Naming

❌ const d = new Date();
   const temp = getUser();
   const flag = true;

✅ const createdAt = new Date();
   const currentUser = getUser();
   const isAuthenticated = true;

3. God Functions

❌ function processOrder(order) {
     // 200 lines: validate, calculate, save, email, log...
   }

✅ function processOrder(order) {
     validateOrder(order);
     const total = calculateTotal(order);
     await saveOrder(order, total);
     await sendConfirmationEmail(order);
     logOrderProcessed(order);
   }

4. Deep Nesting

❌ function check(user) {
     if (user) {
       if (user.active) {
         if (user.role === 'admin') {
           return true;
         }
       }
     }
     return false;
   }

✅ function check(user) {
     if (!user) return false;
     if (!user.active) return false;
     if (user.role !== 'admin') return false;
     return true;
   }

5. Premature Abstraction

❌ // Used once, but has 10 configuration options
   createFlexibleReusableButton({ ... });

✅ // Just make the button
   <button className="primary">Submit</button>

   // Abstract when you need it 3+ times

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SOLID Principles Quick Check

| Principle | Question | Red Flag | |-----------|----------|----------| | **S**ingle Responsibility | "Does this class/function do one thing?" | Class with 10+ methods | | **O**pen/Closed | "Can I extend without modifying?" | Switch statements for types | | **L**iskov Substitution | "Can I swap implementations?" | Overriding methods that break contracts | | **I**nterface Segregation | "Are interfaces focused?" | Clients forced to depend on unused methods | | **D**ependency Inversion | "Do high-level modules depend on abstractions?" | Direct instantiation of dependencies |

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Socratic Questions

Ask the junior these questions instead of giving answers:

1. **Naming**: "Would a new developer understand this name without context?" 2. **Function Size**: "Can you describe what this function does in one sentence?" 3. **Duplication**: "I see this pattern in three places. What happens if it needs to change?" 4. **Abstraction**: "How many times is this abstraction actually used?" 5. **Readability**: "If you came back to this code in 6 months, would you understand it?"

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Naming Conventions

| Type | Convention | Example | |------|------------|---------| | Variables | camelCase | `userName`, `isActive` | | Constants | UPPER_SNAKE_CASE | `MAX_RETRIES`, `API_URL` | | Functions | camelCase + verb | `getUser()`, `handleSubmit()` | | Classes | PascalCase | `UserService`, `AuthProvider` | | Files (components) | PascalCase | `UserProfile.tsx` | | Files (utilities) | camelCase | `formatDate.ts` |

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Standards Reference

See detailed patterns in:

• `/standards/global/naming-conventions.md`

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Red Flags to Call Out

| Flag | Question to Ask | |------|-----------------| | Single letter variables | "What does `d` represent?" | | Functions > 30 lines | "Can we break this into smaller functions?" | | > 3 levels of nesting | "Can we use early returns?" | | Copy-pasted code | "If this logic changes, how many places need updating?" | | Commented-out code | "Is this needed? Can we delete it?" | | TODO without tracking | "Is there a ticket for this?" | | Magic strings/numbers | "Should this be a named constant?" |