A printf with dependant types in TypeScript, similar to Idris (https://gist.github.com/chrisdone/672efcd784528b7d0b7e17ad9c115292)

log.ts

type FieldType<Field> = 
  's' extends Field ? string :
  'f' extends Field ? number :
  'i' extends Field ? number :
  'd' extends Field ? number :
  'o' extends Field ? HTMLElement :
  'O' extends Field ? object :
  'c' extends Field ? string :
  never;

type ExtractFields<T> =
    T extends `${infer _}%${infer Field}${infer R}` ? [FieldType<Field>, ...ExtractFields<R>] :
    T extends `${infer _}%${infer Field}` ? [FieldType<Field>] :
    [];

function log<Fmt extends string>(
  fmt: Fmt,
  ...args: ExtractFields<Fmt>
): void {
  console.log(fmt, ...args);
};

log("Stuff: %s %f %O", 'Hello', 123, { ok: true });