Don’t Consider Migration Complete Until You Enable noImplicitAny

Overview

noImplicitAny is the cornerstone of TypeScript’s type safety. When disabled, TypeScript silently gives variables the any type when it can’t infer a type. This defeats the purpose of TypeScript. Don’t consider your migration complete until you’ve enabled noImplicitAny and eliminated all implicit anys.

When to Use This Skill

• Finishing TypeScript migration
• Enabling strict mode
• Finalizing tsconfig configuration
• Ensuring type safety
• Completing TypeScript adoption

The Iron Rule

Enable noImplicitAny to complete your TypeScript migration. Eliminate all implicit anys for full type safety.

Example

// With noImplicitAny: false (default during migration)
function parse(data) {
  // data is implicitly any - no error!
  return data.json();
}

// With noImplicitAny: true
function parse(data) {
  // Error: Parameter 'data' implicitly has an 'any' type
  return data.json();
}

// Fixed with explicit type
function parse(data: string): unknown {
  return JSON.parse(data);
}

Enabling Strict Mode

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictBindCallApply": true,
    "strictPropertyInitialization": true,
    "noImplicitThis": true,
    "alwaysStrict": true
  }
}

Reference

• Effective TypeScript, 2nd Edition by Dan Vanderkam
• Item 83: Don’t Consider Migration Complete Until You Enable noImplicitAny