Modern JavaScript Patterns

Comprehensive guide for mastering modern JavaScript (ES6+) features, functional programming patterns, and best practices for writing clean, maintainable, and performant code.

Use this skill when

• Refactoring legacy JavaScript to modern syntax
• Implementing functional programming patterns
• Optimizing JavaScript performance
• Writing maintainable and readable code
• Working with asynchronous operations
• Building modern web applications
• Migrating from callbacks to Promises/async-await
• Implementing data transformation pipelines

Do not use this skill when

• The task is unrelated to modern javascript patterns
• You need a different domain or tool outside this scope

Instructions

• Clarify goals, constraints, and required inputs.
• Apply relevant best practices and validate outcomes.
• Provide actionable steps and verification.
• If detailed examples are required, open resources/implementation-playbook.md.

Resources

• resources/implementation-playbook.md for detailed patterns and examples.

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.

Example boundaries

Code blocks are independent illustrations and can redeclare names; they are not one runnable application. The class example deliberately rejects password operations: private fields and string prefixes are not credential hashing. The highlighting helper escapes interpolated values for HTML text only; keep literal templates trusted and do not reuse it for attributes, URLs or scripts. Fetch resolves on HTTP errors: check response.ok, validate response data, and apply explicit deadlines and cancellation; the retry helper only retries network failures. Pagination needs a page/record cap and repeat-page detection. JSON cloning/memoization loses or rejects non-JSON values and cycles; memoized keys also need bounded storage and receiver/purity rules. A timeout race does not abort network work; propagate an AbortSignal when supported.