How do I unwrap/yield the value inside that promise

You can do it with async/await.Don’t be fooled into thinking that you just went from async to sync, async await it is just a wrapper around .then.

functionA(): Promise<string> {
   // api call returns Promise<string>
}

async functionB(): Promise<string> {
   const value = await this.functionA() // how to unwrap the value inside this  promise
   return value;
}

Further

• TypeScript Deep Dive docs