TypeScript 5 New Features - Faster and More User-Friendly Evolution

TypeScript 5 Overview

TypeScript 5 is a major release with significant performance improvements and new features. It includes faster build speeds, new decorator syntax, and enhanced type system.

Official Decorator Support

New decorator syntax compliant with the ECMAScript decorator proposal (Stage 3) is now available.

function logged(originalMethod: any, context: ClassMethodDecoratorContext) {
  const methodName = String(context.name);

  return function (this: any, ...args: any[]) {
    console.log(`Calling ${methodName} with`, args);
    const result = originalMethod.call(this, ...args);
    console.log(`${methodName} returned`, result);
    return result;
  };
}

class Calculator {
  @logged
  add(a: number, b: number): number {
    return a + b;
  }
}

Difference from before: The experimentalDecorators flag is no longer required, and you can use the new standard decorators.

const Type Parameters

Literal types can now be inferred more easily.

// Traditional
function getConfig<T extends readonly string[]>(items: T): T {
  return items;
}
const config = getConfig(['a', 'b', 'c'] as const);

// TypeScript 5
function getConfig<const T extends readonly string[]>(items: T): T {
  return items;
}
const config = getConfig(['a', 'b', 'c']); // No need for as const
// Type: readonly ['a', 'b', 'c']

Performance Improvements

TypeScript 5 achieves significant speedup through internal structure optimization.

Other New Features

All Enums as Union Types

enum Color {
  Red,
  Green,
  Blue
}

// Color type is treated as Color.Red | Color.Green | Color.Blue

moduleResolution: bundler

A new module resolution strategy for modern bundlers has been added.

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

Migration Points

• target: ES2022 or later is recommended
• Consider migrating to new decorators
• Utilize moduleResolution: bundler

Summary

TypeScript 5 is a release that achieves both improved developer experience and performance improvements. With the new decorator syntax and const type parameters, you can write more type-safe and expressive code.