Confused about using .ts files with node adapter

[NormandoHall]

I am new to typescript, and I want to refactor and old running javascript kit code to typescript.

I changed a server file in $lib/server/Redis.ts and adjust all the imports.

Ia am using custom node server, with handler.js in it.

Running in dev mode is ok, but after build (without problems) and load handler.js in my custom express server I get this error:

node:internal/errors:496
    ErrorCaptureStackTrace(err);
    ^

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts" for /opt/minerva/devel/src/lib/server/Redis.ts
    at new NodeError (node:internal/errors:405:5)
    at Object.getFileProtocolModuleFormat [as file:] (node:internal/modules/esm/get_format:79:11)
    at defaultGetFormat (node:internal/modules/esm/get_format:124:36)
    at defaultLoad (node:internal/modules/esm/load:89:20)
    at nextLoad (node:internal/modules/esm/loader:163:28)
    at ESMLoader.load (node:internal/modules/esm/loader:603:26)
    at ESMLoader.moduleProvider (node:internal/modules/esm/loader:457:22)
    at new ModuleJob (node:internal/modules/esm/module_job:64:26)
    at #createModuleJob (node:internal/modules/esm/loader:480:17)
    at ESMLoader.getModuleJob (node:internal/modules/esm/loader:434:34) {
  code: 'ERR_UNKNOWN_FILE_EXTENSION'
}

Node.js v18.18.0

Sveltekit v2.5.0

I need to change something when build kit to compile ts files for node adapter?