typescript

name	typescript
description	TypeScript anti-slop guardrails. Use when writing or reviewing .ts, .tsx, and .mts files. Covers patterns that Biome, tsc, and rslint do not catch.
metadata	{"internal":true}

TypeScript Anti-Slop Guardrails

Skip formatting and lint rules — tooling handles those. This skill targets patterns that produce valid-looking but poor-quality code.

When in doubt, copy the local pattern in the file you are editing rather than importing a style from elsewhere.

1. No Restating Comments

Comments that repeat what the next line does are noise. Only comment why, never what.

// wrong
// Set the current file path
context.setFilePath(filePath);
// Initialize the reporter
const reporter = new Reporter(config);

// right — let code speak; comment only non-obvious intent
// Force sequential execution — parallel runs corrupt shared fixture state
context.setFilePath(filePath);
const reporter = new Reporter(config);

Also avoid: section-header comments inside functions (// --- Validate ---), JSDoc that adds nothing beyond the signature, temporal markers (// added for, // Phase 1).

2. No Unnecessary Defensive Code

Do not add runtime checks that the type system already guarantees. Trust the types.

// wrong — param is already typed string
function resolvePattern(pattern: string): string {
  if (typeof pattern !== 'string') {
    throw new Error('pattern must be a string');
  }
  return glob(pattern);
}

// right — trust the type system
function resolvePattern(pattern: string): string {
  return glob(pattern);
}

Also avoid: redundant ?? [] / || {} on fields that are always initialized (normalize once at construction instead), null checks on values you just produced, try/catch around code that cannot throw.

3. Minimize as

Treat as as a last resort, not a way to silence errors. If you need as, the types are probably wrong.

// wrong — casting to escape a type error
const name = (config as any).testName;

// right — narrow or fix the type
if ('testName' in config) {
  const name = config.testName;
}

• Never as any or as unknown as X unless at a proven interop seam or test-only partial mock.
• If control flow already proved the type, the cast is redundant — remove it.
• When a cast is truly needed, add a one-line comment explaining why.

4. Minimize any

noExplicitAny is off in this repository, so self-police. Prefer unknown + narrowing, or a generic, before reaching for any. Never let any leak into exported APIs, config types, or cross-package contracts.

5. No One-Use Abstractions

Do not extract a function, class, or type that is used exactly once, unless it genuinely improves readability at the call site.

// wrong — called once, five lines away
function formatTestName(name: string): string {
  return name.replace(/\.test$/, '');
}
// ... later:
const display = formatTestName(file);

// right — inline it
const display = file.replace(/\.test$/, '');

Also avoid: interfaces with single implementations, factory functions that create one thing, options objects with 10 optional fields for features that don't exist yet.

Threshold: extract when used in 3+ places, or when the extraction meaningfully shortens a complex function.

6. No Catch-and-Rethrow Without Context

If a catch block doesn't add information or recover, delete the try/catch.

// wrong — catches and rethrows with just a message rewrite
try {
  await loadConfig(path);
} catch (error) {
  throw new Error(
    `Failed to load: ${error instanceof Error ? error.message : error}`,
  );
}

// right — use cause to preserve the chain
try {
  await loadConfig(path);
} catch (error) {
  throw new Error(`Failed to load config at ${path}`, { cause: error });
}

// also right — just don't catch if you add nothing
await loadConfig(path);

Also avoid: bare rethrow (catch (e) { throw e; }), empty catch blocks, catch blocks that only console.log.

7. Single Source of Truth — Prevent Drift

When two declarations describe the same thing — types, constants, defaults, validation rules — one must derive from the other. Duplicating independently causes drift: they match today, diverge silently tomorrow. Derive via extends, Pick, ReturnType, typeof, satisfies, or simply importing the canonical definition.

8. Search Before Creating Utilities

Before writing a helper function, search the codebase. If it exists, import it. If it exists but isn't exported, export it. Don't create a second isObject() or normalizeSlashes().

9. No Over-Engineered Types

• Don't introduce deep conditional types, mapped types, or template literal types unless they clearly reduce complexity.
• Don't create a reusable utility type for one call site.
• Prefer the smallest type shape that explains the contract.
• This repository uses both type and interface — follow nearby code.

Repository Conventions

• Use import type for type-only imports.
• Public config properties: use JSDoc with @default.
• Preserve existing file-local patterns unless there is a clear bug or maintenance win.