typescript-type-system

# TypeScript Type System

Master TypeScript's type system features to write type-safe code. This
skill focuses exclusively on TypeScript language capabilities.

## TypeScript Compiler

```bash
# Type check without emitting files
tsc --noEmit

# Type check with specific config
tsc --noEmit -p tsconfig.json

# Show compiler version
tsc --version

# Watch mode for development
tsc --noEmit --watch
```

## Strict Mode Configuration

**tsconfig.json strict mode options:**

```json
{
  "compilerOptions": {
    "strict": true,                           // Enables all strict
    "noImplicitAny": true,                    // Error on 'any'
    "strictNullChecks": true,                 // null must be explicit
    "strictFunctionTypes": true,              // Stricter function types
    "strictBindCallApply": true,              // Strict bind/call/apply
    "strictPropertyInitialization": true,     // Class init required
    "noImplicitThis": true,                   // Error on 'this' any
    "alwaysStrict": true,                     // Parse strict mode
    "useUnknownInCatchVariables": true        // Catch is 'unknown'
  }
}
```

## Essential Compiler Options

```json
{
  "compilerOptions": {
    // Type Checking
    "exactOptionalPropertyTypes": true,       // Distinguish undefined from missing
    "noFallthroughCasesInSwitch": true,      // Prevent fallthrough in switch
    "noImplicitOverride": true,               // Require 'override' keyword
    "noImplicitReturns": true,                // All code paths must return
    "noPropertyAccessFromIndexSignature": true, // Require bracket notation for index
    "noUncheckedIndexedAccess": true,         // Index signatures return T | undefined
    "noUnusedLocals": true,                   // Error on unused local variables
    "noUnusedParameters": true,               // Error on unused parameters

    // Module Resolution
    "moduleResolution": "bundler",            // Modern bundler resolution
    "resolveJsonModule": true,