AgentSkillsCN

prefer-unknown-over-any

在 TypeScript 中，对于类型未知的值，优先使用 unknown 而非 any，以实现更安全的类型处理。

SKILL.md
--- frontmatter
name: prefer-unknown-over-any
description: Use unknown instead of any for type-safe handling of values with unknown types in TypeScript.

Prefer unknown Over any

Rule

Use unknown to force type checking before usage. Never use any.

✅ Good (unknown)

typescript
function processData(data: unknown) {
  if (typeof data === "string") {
    return data.toUpperCase(); // OK - type narrowed
  }
  throw new Error("Expected string");
}

❌ Bad (any)

typescript
function processData(data: any) {
  return data.toUpperCase(); // No error, but might crash at runtime
}

Why unknown?

  • •Forces type guards before use
  • •Prevents runtime errors
  • •Maintains type safety
  • •Makes invalid states unrepresentable

Common Type Guards

typescript
// typeof check
if (typeof value === "string") { /* ... */ }

// instanceof check
if (value instanceof Error) { /* ... */ }

// in operator
if (typeof value === "object" && value !== null && "prop" in value) { /* ... */ }

// Custom type guard
function isUser(value: unknown): value is User {
  return typeof value === "object" && value !== null && "name" in value;
}