JavaScript and TypeScript Best Practices

Comprehensive coding standards for JavaScript and TypeScript applications, designed for AI agents and LLMs working with modern JavaScript/TypeScript codebases.

Note: This skill focuses on general best practices, TypeScript patterns, and safety. For performance optimization, use the accelint-ts-performance skill instead.

When to Use This Skill

This skill provides expert-level patterns for JavaScript and TypeScript code. Load AGENTS.md to scan rule summaries and identify relevant optimizations for your task.

How to Use

This skill uses a progressive disclosure structure to minimize context usage:

1. Start with the Overview (AGENTS.md)

Read AGENTS.md for a concise overview of all rules with one-line summaries organized by category.

2. Load Specific Rules as Needed

When you identify a relevant pattern or issue, load the corresponding reference file for detailed implementation guidance:

Quick Start:

• quick-start.md - Complete workflow examples with before/after code

General Best Practices:

• naming-conventions.md - Descriptive names, qualifier ordering, boolean prefixes
• functions.md - Function size, parameters, explicit values
• control-flow.md - Early returns, flat structure, block style
• state-management.md - const vs let, immutability, pure functions
• return-values.md - Return zero values instead of null/undefined
• misc.md - Line endings, defensive programming, technical debt
• code-duplication.md - Extract common patterns, DRY principle, when to consolidate

TypeScript:

• any.md - Avoid any, use unknown or generics
• enums.md - Use as const objects instead of enum
• type-vs-interface.md - Prefer type over interface
• bundler-paths.md - Use statically analyzable import and file-system paths for optimal bundling

Safety:

• input-validation.md - Validate external data with schemas
• assertions.md - Split assertions, include values
• error-handling.md - Handle all errors explicitly
• error-messages.md - User-friendly vs developer-specific messages

Performance:

• For performance optimization tasks, use the accelint-ts-performance skill for comprehensive profiling workflows and optimization patterns

Documentation:

• For documentation tasks, use the accelint-ts-documentation skill for comprehensive JSDoc and comment guidance

3. Apply the Pattern

Each reference file contains:

• ❌ Incorrect examples showing the anti-pattern
• ✅ Correct examples showing the optimal implementation
• Explanations of why the pattern matters

4. Use the Report Template

When this skill is invoked, use the standardized report format:

Template: assets/output-report-template.md

The report format provides:

• Executive Summary with impact assessment
• Severity levels (Critical, High, Medium, Low) for prioritization
• Impact analysis (potential bugs, type safety, maintainability, runtime failures)
• Categorization (Type Safety, Safety, State Management, Return Values, Code Quality)
• Pattern references linking to detailed guidance in references/
• Phase 2 summary table for tracking all issues

When to use the audit template:

• Skill invoked directly via /accelint-ts-best-practices <path>
• User asks to "review code quality" or "audit code" across file(s), invoking skill implicitly

When NOT to use the report template:

• User asks to "fix this type error" (direct implementation)
• User asks "what's wrong with this code?" (answer the question)
• User requests specific fixes (apply fixes directly without formal report)