using typescript playground to make sense of code

I came across the following function in a codebase today and struggled to see what was happening - the combination of classes with typescript was just too much to process today.

export const SvcBuilder = <T extends resources.BaseResource>(
  config: ResourceConfig<T>,
): new (pool: pg.Pool, mode?: ResourceServiceMode) => BaseResourceService<T> =>
  class extends BaseResourceService<T> {
    constructor(pool: pg.Pool, mode?: ResourceServiceMode) {
      super(config, pool, mode)
    }
  }

In particular, I couldn’t quite place what new (pool: pg.Pool, mode?: ResourceServiceMode) applied to.

I struggled to write my own pure JS function for a while, but kept running into trouble. Eventually I remembered the Typescript Playground. It’s a site that will show Typescript code side-by-side with the vanilla JS it compiles down into.

Hopefully next time I remember a little faster so as to not spend so much time before getting to the answer!

For what it’s worth - it was referring to the signature of instantiating the returned class. The more you know!