Mastering TypeScript 5: Features You Should Know

TypeScript 5 brings a wealth of new features that improve developer productivity and code safety. Here are the ones I find most useful.

Decorators

TypeScript 5 includes the stage 3 decorators proposal, which provides a more ergonomic way to modify classes and their members:

function log(target: any, context: ClassMethodDecoratorContext) {
  const methodName = String(context.name)

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

  return replacementMethod
}

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

Const Type Parameters

Const type parameters allow you to infer the most specific type possible:

function tuple<T extends readonly string[]>(...items: T): T {
  return items
}

// Inferred as readonly ["hello", "world"]
const result = tuple("hello", "world")

Improved Module Resolution

TypeScript 5 improves module resolution to better match modern bundlers like webpack and esbuild. The bundler module resolution strategy understands package.json exports and imports fields.

Conclusion

TypeScript continues to evolve with features that make type-safe JavaScript development more productive. The improvements in version 5 are well worth adopting in your projects.