Partial<T> and Required<T>

Syntax

Partial<Type>
Required<Type>

Examples

interface User {
  id: number;
  name: string;
  email: string;
}

function updateUser(id: number, updates: Partial<User>): void {
  // updates can include ANY subset of User's properties
  console.log(`Updating user ${id}:`, updates);
}

updateUser(1, { name: "New Name" });          // OK - only updating name
updateUser(1, { email: "new@example.com" });   // OK - only updating email

interface Config {
  host?: string;
  port?: number;
  timeout?: number;
}

function startServer(config: Required<Config>): void {
  // every property is guaranteed to be present here, not optional
  console.log(`Starting on ${config.host}:${config.port}`);
}

// startServer({ host: "localhost" }); // Error - port and timeout are missing
startServer({ host: "localhost", port: 3000, timeout: 5000 }); // OK

Best practices

• Use Partial<T> for update/patch functions where the caller should be able to supply any subset of an object's fields
• Use Required<T> at boundaries where a fully-populated object is genuinely necessary, even if the original type allows optional fields elsewhere
• Avoid using Partial<T> for creating brand-new objects when most fields are actually required - it can hide missing-field bugs that a stricter type would catch
• Combine Partial<T> with a spread merge pattern ({ ...existing, ...updates }) for a clean, type-safe update implementation

At a glance

Purpose

Static types for JavaScript

File extension

.ts · .tsx

Runs in

Compiled to JavaScript

Usually used with

JavaScript and its ecosystem

Specifications & further reading

• TypeScript Handbook

Related TypeScript documentation