From TypeScript to Havran, file by file

Adopting a new language usually means a big-bang rewrite. Havran is designed to avoid that entirely: it reads 100% of your TypeScript and JavaScript, and the code it generates is just TypeScript. You can convert a single file and leave the rest untouched.

Step 1: rename and relax

Start by translating one module. Most TypeScript maps over almost mechanically:

data class Product(val id: Long, val name: String, val price: Double)

fun total(items: List<Product>): Double =
  items.sumOf { it.price }

interface Product {
  readonly id: number
  readonly name: string
  readonly price: number
}

function total(items: ReadonlyArray<Product>): number {
  let acc = 0
  for (let i = 0; i < items.length; i++) acc += items[i].price
  return acc
}

Note the iteration lowers to an indexed for loop, not .reduce() — faster, and easier for engines to optimize.

Step 2: keep your imports

Havran imports your existing packages with no shims:

import { z } from "zod"

val schema = z.object(name = z.string())

What stays the same

• Your bundler, test runner, and CI — unchanged.
• Your node_modules — consumed directly, types and all.
• Your output — ordinary .js + .d.ts .

What gets better

Migrate at your own pace. There's no point of no return.

When you're ready, convert the next file. That's the whole migration story.