typescript-strict-typing

TypeScript Strict Typing Standards

CRITICAL: This skill applies to ALL TypeScript code writing scenarios - not just when fixing type errors.

When to Use This Skill

✅ ALWAYS use when:

• Writing any TypeScript code
• Implementing new features
• Fixing bugs
• Refactoring code
• Modifying existing code
• Adding new functions, classes, or modules
• Working with third-party libraries
• Handling async operations
• Processing data structures

Absolutely Prohibited Patterns

❌ 1. Type Escape Mechanisms

Never use these under any circumstances:

// ❌ WRONG - any type
const data: any = fetchData()

// ❌ WRONG - type assertion
const element = document.getElementById('id') as HTMLInputElement

// ❌ WRONG - double assertion
const value = something as unknown as SomeType

// ❌ WRONG - TypeScript suppression comments
// @ts-ignore
// @ts-expect-error

// ❌ WRONG - ESLint suppression comments for type rules
// eslint-disable-next-line @typescript-eslint/no-explicit-any
// eslint-disable-next-line @typescript-eslint/ban-types
// eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
// eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
// eslint-disable-next-line @typescript-eslint/no-unsafe-call
// eslint-disable-next-line @typescript-eslint/no-unsafe-return
/* eslint-disable @typescript-eslint/no-explicit-any */

// ❌ WRONG - ESLint config files that disable type safety rules
// .eslintrc.js with rules turned off

❌ 2. Non-null Assertion Operator (!)

// ❌ WRONG - non-null assertion
const value = array.find(x => x.id === id)!.name

// ❌ WRONG - property access assertion
const result = obj!.property

// ✅ CORRECT - proper null checking
const item = array.find(x => x.id === id)
if (item) {
  const value = item.name
}

❌ 3. Implicit Any

// ❌ WRONG - implicit any parameters
function process(data) {
  return data.value
}

// ❌ WRONG - implicit any return
function getData() {
  return fetchSomething()
}

// ✅ CORRECT - explicit types
function process(data: DataType): string {
  return data.value
}

function getData(): Promise<DataType> {
  return fetchSomething()
}