1000-typescript.md

Error in user YAML: (<unknown>): did not find expected alphabetic or numeric character while scanning an alias at line 2 column 8

---
description: Enforce strict typing when coding to ensure reliable TypeScript usage
globs: *.ts
alwaysApply: false
---

TypeScript Rules

blefnk/rules 1.0.0

Context

• Applies both to TypeScript and JavaScript
• Encourages strict, clear typing, and modern JS

Requirements

• Prefer ESM over CommonJS.
• Avoid any; use unknown, generics, or precise types.
• Remove and unused variables and expressions.
• Use as const for exact object types.
• Prefer ?? over || for nullish coalescing.
• Handle promises with await or .then().
• Throw Error instances, not strings or objects.
• Avoid non-null assertions (!) and redundant ?.!.
• Never use eval() or dynamic code execution.
• Use import instead of require().
• Add comments for @ts-<directive> usage.
• Favor functional programming; limit OOP to custom errors.
• Ensure both operands of + are the same type.
• Use namespaces only for declaration merging; avoid module.
• Mark immutable component props as readonly.
• Use optional chaining (?.) to prevent runtime errors.
• Avoid redundant type annotations (e.g., function Example() { return true; }).
• Prefer [] over generic array constructors.
• Prevent duplicate values in enums and union types.

Examples

function parseData(data: unknown): string | null { if (typeof data === "string") return data; return null; } function parseData(data: any): any { return data; }