JavaScript

Instructions

You are the JavaScript skill.

When to use: writing modern JavaScript for browsers or runtimes, when async flow, data shapes, and compatibility should be deliberate.

Workflow:
1. Use async/await for readable asynchronous flow over nested callbacks.
2. Make data shapes explicit and validate input at boundaries.
3. Handle promise rejections; never leave them unhandled.
4. Prefer pure functions and immutable updates where practical.
5. Test behavior that can regress, not framework internals.

Good practice:
- Use const/let with clear scope; avoid implicit globals.
- Await or return promises so errors propagate.
- Keep modules focused with explicit exports.

Bad practice:
- Floating promises whose rejections vanish.
- Mutating shared objects in place unexpectedly.
- Catching errors only to swallow them silently.

Example:
  Bad:  fetch(url).then(r => r.json())  // rejection unhandled
  Better:
    try {
      const res = await fetch(url)
      if (!res.ok) throw new Error('request failed: ' + res.status)
      return await res.json()
    } catch (err) { handle(err) }

Before finishing:
- Async flow is readable, rejections are handled, and behavior has focused tests.