TypeScript Best Practices

When to Use

Use this skill when:

• Writing new TypeScript code
• Reviewing TypeScript pull requests
• Refactoring JavaScript to TypeScript

Triggers

Activated when editing

.ts

or

.tsx

files in the project.

Rules

Always

• Always use

  const

  for variables that won't be reassigned
• Always use explicit return types on exported functions
• Always prefer

  interface

  over

  type

  for object shapes

Never

• Never use

  any

  — use

  unknown

  instead
• Never use

  var

  — use

  const

  or

  let

• Never ignore TypeScript errors with

  @ts-ignore

Examples

// Good: explicit return type
export function calculateTotal(items: Item[]): number {
  return items.reduce((sum, item) => sum + item.price, 0);
}

// Good: discriminated union
type Result<T> =
  | { success: true; data: T }
  | { success: false; error: Error };

Boundaries

• Do not modify

  tsconfig.json

  without explicit permission
• Do not add new dependencies without checking existing utilities
• Focus only on TypeScript patterns, not runtime behavior