TypeScript 5 Updates – New Features, Enhancements, and Breaking Changes

Introduction – What’s New in TypeScript 5?

TypeScript 5 brings a wave of exciting improvements, better performance, and long-awaited features that simplify code and make the developer experience even better. This version focuses on language ergonomics, compiler speed, and modern JavaScript compatibility, marking a major leap forward for TypeScript’s evolution.

In this guide, you’ll learn:

• What’s new in TypeScript 5
• Key feature highlights with examples
• Breaking changes and migration notes
• Performance and tooling enhancements

Why Upgrade to TypeScript 5?

Key Features in TypeScript 5

1️⃣ Standard ECMAScript Decorators

Decorators are now based on the official ECMAScript proposal, replacing the experimental legacy version.

function log(target: any, key: string | symbol) {
  console.log(`Decorated: ${String(key)}`);
}

class Example {
  @log
  sayHello() {
    console.log("Hello");
  }
}

What’s new?

• Decorators are now part of the ECMAScript standard
• Use "experimentalDecorators": false (no longer required)
• TypeScript 5 aligns with other platforms and browsers using native decorators

2️⃣ Const Type Parameters

You can now mark generic parameters as const, which preserves literal types.

function freeze<const T extends object>(obj: T): Readonly<T> {
  return Object.freeze(obj);
}

const result = freeze({ role: "admin" });
// type is { readonly role: "admin" }, not { role: string }

This allows tighter control of generic types and better inference.

3️⃣ Faster and Leaner Compiler

• TypeScript 5 includes internal compiler rewrites that improve startup time and memory usage.
• Compiles large projects up to 10–20% faster in benchmark testing.
• Compiler size is smaller, reducing dependency bloat in CI/CD pipelines.

4️⃣ No More Node.js Type Package by Default

TypeScript no longer automatically includes types for Node.js. This makes TypeScript more environment-agnostic.

npm install --save-dev @types/node

Useful if you’re building a frontend-only app (e.g., with React or Vue).

5️⃣ Resolution Customization with moduleResolution: "bundler"

{
  "compilerOptions": {
    "moduleResolution": "bundler"
  }
}

New module resolution strategy optimized for ESM bundlers like Vite and Rollup.

• Supports "exports" and "imports" fields in package.json
• Improves compatibility with modern JS libraries
• Avoids fallback to CommonJS types when not needed

6️⃣ 🪄 New extends Constraints in Infer Types

You can now use extends directly within infer clauses inside conditional types.

type ExtractString<T> = T extends infer U extends string ? U : never;

type Result = ExtractString<"hello" | 42>; // "hello"

Enables advanced pattern matching in generic types.

7️⃣ Better IntelliSense for JSDoc and JavaScript

TypeScript 5 enhances JSDoc support for JavaScript files:

/**
 * @param {number} a
 * @param {number} b
 * @returns {number}
 */
function add(a, b) {
  return a + b;
}

• More accurate suggestions
• Improved type inference in .js projects
• Boosts developer experience without converting everything to .ts

Breaking Changes in TypeScript 5

Use --strict and type-check before upgrading to avoid runtime surprises.

tsconfig.json Enhancements

Recommended tsconfig.json for TypeScript 5

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "ESNext",
    "moduleResolution": "bundler",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "useDefineForClassFields": true
  }
}

• useDefineForClassFields now reflects the standardized ECMAScript behavior.
• moduleResolution: "bundler" helps integrate smoothly with modern build tools.

Summary – TypeScript 5 Updates

TypeScript 5 introduces several modern features that improve performance, simplify project setup, and bring the language closer to ECMAScript standards. It’s one of the most important updates for long-term maintainability and alignment with JavaScript’s evolution.

Key Takeaways:

• Decorators are now standardized — no more experimental flags
• Const type parameters improve type inference
• Faster compiler performance and smaller install size
• Modern module resolution for bundlers (like Vite)
• Breaking changes removed legacy features for better standard compliance

Real-world impact:

• Better build speed for large monorepos
• Cleaner code with fewer workarounds
• Improved compatibility with modern tooling and frontend frameworks

FAQs – TypeScript 5 Updates

Do I need to refactor my decorators for TypeScript 5?

Yes, if you were using the legacy decorator proposal. TypeScript 5 supports standardized ECMAScript decorators.

What is const in type parameters?

It’s a new feature that preserves literal types in generics, offering better precision and less widening.

Will TypeScript 5 break existing projects?

Not if you’re using standard features. But decorators and module resolution may need updates if you’re using experimental configurations.

How does moduleResolution: "bundler" help?

It optimizes import resolution for tools like Vite, Rollup, and ESBuild, aligning with modern ESM practices.

Is it safe to upgrade to TypeScript 5 now?

Yes, after testing your codebase and ensuring all dependencies are compatible, TypeScript 5 provides long-term stability and performance benefits.