How to fix 'exactOptionalPropertyTypes' requires strict mode in TypeScript

interface User {
  email?: string;
}

// All of these are valid:
const user1: User = {};                    // email omitted
const user2: User = { email: "[email protected]" };  // email present
const user3: User = { email: undefined };  // email explicitly undefined

// The property exists with value undefined:
console.log("email" in user3);  // true

interface User {
  email?: string;
}

const user1: User = {};  // OK - email omitted
const user2: User = { email: "[email protected]" };  // OK
const user3: User = { email: undefined };
// Error: Type 'undefined' is not assignable to type 'string'
// with 'exactOptionalPropertyTypes: true'

// To allow explicit undefined, add it to the type:
interface User {
  email?: string | undefined;  // Now explicit undefined is allowed
}

// With strictNullChecks: false
let name: string = undefined;  // Allowed (unsafe!)

{
  "compilerOptions": {
    "strict": true
  }
}

// Temporary suppression during migration
// @ts-expect-error - TODO: Fix null handling
const value: string = potentiallyNull;

{
  "compilerOptions": {
    "strict": true,
    "exactOptionalPropertyTypes": true
  }
}

// Before
interface Config {
  timeout?: number;
}

function reset(config: Config) {
  config.timeout = undefined;  // Error with exactOptionalPropertyTypes
}

// Fix option 1: Delete the property
function reset(config: Config) {
  delete config.timeout;
}

// Fix option 2: Allow undefined explicitly
interface Config {
  timeout?: number | undefined;
}

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "node16",
    "moduleResolution": "node16",
    "lib": ["ES2022"],

    // Strict type checking
    "strict": true,
    "exactOptionalPropertyTypes": true,
    "noUncheckedIndexedAccess": true,
    "noPropertyAccessFromIndexSignature": true,

    // Additional strictness
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "allowUnusedLabels": false,

    // Emit
    "declaration": true,
    "sourceMap": true,
    "outDir": "./dist",

    // Other
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  }
}

// Error in @types/some-library

{
  "compilerOptions": {
    "skipLibCheck": true  // Ignore errors in .d.ts files
  }
}

// types/library-fixes.d.ts
declare module "problematic-library" {
  export interface Config {
    option?: string | undefined;  // Add explicit undefined
  }
}