Comment renvoyer une valeur résolue à partir d'une fonction asynchrone dans une autre fonction asynchrone ?

class Posts {
  constructor(url) {
    this.ready = false
    this.data = {}
    this.url = url
  }
  async init() {
      try { 
        let res = await fetch( this.url )
        if (res.ok) {
            let data = await res.json()

          // Do bunch of transformation stuff here

          this.data = data
          this.ready = true
          return this.getPostById(4)  // Return the value of getPostById()
        }
      } 
      catch (e) { 
         console.log(e)
      }
  }
  getPostById(id){
     return this.data.find( p => p.id === id )
  }
}  

let myFunc = async () => {
   const postId = 4
   await allPosts.init()  // I need to wait for this to finish before returning

   // This is logging correct value
   console.log( 'logging: ' + JSON.stringify(allPosts.getPostById( postId ), null, 4) )

   // Return the RESULT of allPosts.getPostById( postId ) ???
   return await allPosts.getPostById( postId )
}