---
title: "Code Quality Checklist"
description: "- **Swallowed exceptions**: Empty catch blocks or catch with only logging. Example: ```javascript try { ... } catch (e) { } // Silent failure try { ... } catch (e) { console.log(e) } // Log and forget ``` - **Overly broad catch**: Catching `Exception`/`Error` base class instead of specific types - **Error information leakage**: Stack traces or internal details exposed to users - **Missing error ha"
type: skill
canonical_url: https://claudary.paisolsolutions.com/skills/code-quality-checklist-1
source: "Claudary"
difficulty: intermediate
author: "Claude Code Knowledge Pack"
date: 2026-07-10T11:14:08.830Z
license: CC-BY-4.0
attribution: "Code Quality Checklist — Claudary (https://claudary.paisolsolutions.com/skills/code-quality-checklist-1)"
---

# Code Quality Checklist
- **Swallowed exceptions**: Empty catch blocks or catch with only logging. Example: ```javascript try { ... } catch (e) { } // Silent failure try { ... } catch (e) { console.log(e) } // Log and forget ``` - **Overly broad catch**: Catching `Exception`/`Error` base class instead of specific types - **Error information leakage**: Stack traces or internal details exposed to users - **Missing error ha

## Overview

# Code Quality Checklist

## Contents
- Error Handling (anti-patterns, best practices, questions)
- Performance & Caching (CPU, database/IO, caching, memory)
- Boundary Conditions (null/undefined, empty collections, numeric, string)

## Error Handling

### Anti-patterns to Flag

- **Swallowed exceptions**: Empty catch blocks or catch with only logging. Example:
  ```javascript
  try { ... } catch (e) { }  // Silent failure
  try { ... } catch (e) { console.log(e) }  // Log and forget
  ```
- **Overly broad catch**: Catching `Exception`/`Error` base class instead of specific types
- **Error information leakage**: Stack traces or internal details exposed to users
- **Missing error handling**: No try-catch around fallible operations (I/O, network, parsing)
- **Async error handling**: Unhandled promise rejections, missing `.catch()`, no error boundary

### Best Practices to Check

- [ ] Errors are caught at appropriate boundaries
- [ ] Error messages are user-friendly (no internal details exposed)
- [ ] Errors are logged with sufficient context for debugging
- [ ] Async errors are properly propagated or handled
- [ ] Fallback behavior is defined for recoverable errors
- [ ] Critical errors trigger alerts/monitoring

### Questions to Ask
- "What happens when this operation fails?"
- "Will the caller know something went wrong?"
- "Is there enough context to debug this error?"

---

## Performance & Caching

### CPU-Intensive Operations

- **Expensive operations in hot paths**: Regex compilation, JSON parsing, crypto in loops
- **Blocking main thread**: Sync I/O, heavy computation without worker/async
- **Unnecessary recomputation**: Same calculation done multiple times
- **Missing memoization**: Pure functions called repeatedly with same inputs

### Database & I/O

- **N+1 queries**: Loop that makes a query per item instead of batch
  ```javascript
  // Bad: N+1
  for (const id of ids) {
    const user = await db.query(`SELECT * FROM users WHERE id = ?`, id)
  }
  // Good: Batch
  const users = await db.query(`SELECT * FROM users WHERE id IN (?)`, ids)
  ```
- **Missing indexes**: Queries on unindexed columns
- **Over-fetching**: SELECT * when only few columns needed
- **No pagination**: Loading entire dataset into memory

### Caching Issues

- **Missing cache for expensive operations**: Repeated API calls, DB queries, computations
- **Cache without TTL**: Stale data served indefinitely
- **Cache without invalidation strategy**: Data updated but cache not cleared
- **Cache key collisions**: Insufficient key uniqueness
- **Caching user-specific data globally**: Security/privacy issue

### Memory

- **Unbounded collections**: Arrays/maps that grow without limit
- **Large object retention**: Holding references preventing GC
- **String concatenation in loops**: Use StringBuilder/join instead
- **Loading large files entirely**: Use streaming instead

### Questions to Ask
- "What's the time complexity of this operation?"
- "How does this behave with 10x/100x data?"
- "Is this result cacheable? Should it be?"
- "Can this be batched instead of one-by-one?"

---

## Boundary Conditions

### Null/Undefined Handling

- **Missing null checks**: Accessing properties on potentially null objects
- **Truthy/falsy confusion**: `if (value)` when `0` or `""` are valid
- **Optional chaining overuse**: `a?.b?.c?.d` hiding structural issues
- **Null vs undefined inconsistency**: Mixed usage without clear convention

### Empty Collections

- **Empty array not handled**: Code assumes array has items
- **Empty object edge case**: `for...in` or `Object.keys` on empty object
- **First/last element access**: `arr[0]` or `arr[arr.length-1]` without length check

### Numeric Boundaries

- **Division by zero**: Missing check before division
- **Integer overflow**: Large numbers exceeding safe integer range
- **Floating point comparison**: Using `===` instead of epsilon comparison
- **Negative values**: Index or count that shouldn't be negative
- **Off-by-one errors**: Loop bounds, array slicing, pagination

### String Boundaries

- **Empty string**: Not handled as edge case
- **Whitespace-only string**: Passes truthy check but is effectively empty
- **Very long strings**: No length limits causing memory/display issues
- **Unicode edge cases**: Emoji, RTL text, combining characters

### Common Patterns to Flag

```javascript
// Dangerous: no null check
const name = user.profile.name

// Dangerous: array access without check
const first = items[0]

// Dangerous: division without check
const avg = total / count

// Dangerous: truthy check excludes valid values
if (value) { ... }  // fails for 0, "", false
```

### Questions to Ask
- "What if this is null/undefined?"
- "What if this collection is empty?"
- "What's the valid range for this number?"
- "What happens at the boundaries (0, -1, MAX_INT)?"

---

Source: [Claudary](https://claudary.paisolsolutions.com/skills/code-quality-checklist-1) · https://claudary.paisolsolutions.com