Agent Skills: JavaScript Language Patterns

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

// Modern Syntax
const [x, ...rest] = items;
const name = user?.profile?.name ?? 'Guest';

// Async + Error Handling
async function getUser(id) {
  const res = await fetch(`/api/${id}`);
  return res.json(); // Errors propagate
}

// Private Fields
class Service {
  #key;
  constructor(k) {
    this.#key = k;
  }
}

Reference & Examples

For advanced patterns and functional programming: See references/REFERENCE.md.

Related Topics

best-practices | tooling