JavaScript Language Patterns

Priority: P0 (CRITICAL)

Modern JavaScript standards for clean, maintainable code.

Implementation Guidelines

• Variables: const default. let if needed. No var.
• Functions: Arrows for callbacks. Declarations for top-level.
• Async: async/await + try/catch.
• Objects: Destructuring, Spread ..., Optional Chain ?., Nullish ??.
• Strings: Template literals ${}.
• Arrays: map, filter, reduce. No loops.
• Modules: ESM import/export.
• Classes: Use #private fields.

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
async function getUser(id) {
  try {
    const res = await fetch(`/api/${id}`);
    return res.json();
  } catch (err) {
    console.error(err);
    throw err;
  }
}

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

Reference & Examples

For advanced patterns and functional programming: See [references/REFERENCE.md](references/REFERENCE.md).

Related Topics

best-practices | tooling