TypeScript in 2026: Ubiquitous and Faster Than Ever

TypeScript 5.x is the default for every serious JS project in 2026. The 5.x series focused on three things: standard decorators, type inference improvements, and compile-time performance. Here's what matters in practice.

1. Standard Decorators (TC39 Stage 3)

TypeScript 5.0 replaced the old experimentalDecorators with the TC39-standard version. They're simpler and more predictable:

function log(target: any, context: ClassMethodDecoratorContext) {
  return function (this: any, ...args: any[]) {
    console.log(`Calling ${String(context.name)} with`, args);
    return target.call(this, ...args);
  };
}

class UserService {
  @log
  getUser(id: string) {
    return db.users.findById(id);
  }
}

2. const Type Parameters

Infer literal types without as const scattered everywhere:

function createRoute<const T extends string>(path: T) {
  return { path, handler: null as any } as { path: T; handler: Function };
}

const r = createRoute("/users/:id");
//    r.path is typed as "/users/:id" — not string

3. The satisfies Operator

Validate a value matches a type without widening it:

const config = {
  port: 3000,
  host: "localhost",
  db: { url: "mongodb://..." },
} satisfies AppConfig;

// config.db.url is string — not AppConfig["db"] which might be broader
config.db.url.toUpperCase(); // ✅ works — no type error

4. Improved Type Inference for Methods

TypeScript 5.5+ dramatically improved narrowing in callbacks and method chains — fewer manual type assertions in array operations:

const numbers = [1, 2, null, 3, null, 4];

// Before 5.5 — had to cast
const clean = numbers.filter((n): n is number => n !== null);

// 5.5+ — inferred automatically in many patterns
const clean2 = numbers.filter(Boolean) as number[];

5. Isolated Declarations (5.5)

Force explicit return types on exported functions, enabling parallel type-checking and faster CI builds in monorepos. Enable it in tsconfig.json:

{
  "compilerOptions": {
    "isolatedDeclarations": true
  }
}

Performance Wins

TypeScript 5.x reduced memory usage by ~20% and type-check speed by up to 50% on large codebases through smarter caching and reduced redundant work. If you haven't upgraded, the faster tsc alone is worth it.