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name: javascript-language description: Modern JavaScript (ES2022+) patterns for clean, maintainable code. Use when working with modern JavaScript features like optional chaining, nullish coalescing, or ESM. metadata: triggers: files: - '/*.js' - '/.mjs' - '**/.cjs' keywords: - const - let - arrow - async - await - promise - destructuring - spread - class

JavaScript Language Patterns

Priority: P0 (CRITICAL)

Implementation Guidelines

• Variables: const default. let if needed. No var — block scope only.
• Functionality: Use Arrow Functions for callbacks/inlines; Function Declaration for core logic.
• Async Logic: Use async/await with try/catch and Promise.all() for parallel operations. ESM import/export only. No Callbacks — promisify everything.
• Modern Syntax: Use Destructuring, Spread (...), Optional Chain ?. and Nullish ?? coalescing.
• String Handling: Use Template Literals (backticks) for interpolation and multi-line strings.
• Data Collections: Prefer map, filter, and reduce over imperative for loops.
• Modules: Standardize on ESM import/export; use Named Exports over Default.
• Encapsulation: Leverage #private class fields for encapsulation.
• Error States: Throw new Error() with descriptive messages; never throw strings.

Anti-Patterns

• No var — Block scope only.
• No ==: Strict ===.
• No new Object(): Use literals {}.
• No Callbacks: Promisify everything.
• No Mutation: Immutability first.

Code & Reference

See references/REFERENCE.md for modern syntax, async patterns, private fields, and functional programming examples.

Related Topics

best-practices | tooling

Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

• ESM import/export

• No Callbacks

• No var

• Nullish ??

• Optional Chain ?.

• async/await

• const default

• let if needed

• user?.profile?.name

• Additional task-grounded exact anchors: try/catch