fetchRecursive.js

// async function fetchRefs(obj)

const allPromises = []

;(function fetchRefs(obj) {
  for (let key in obj) {
    if (isRef(obj[key]) {
      const promise = fetchRef(obj[key])
      allPromises.push(promise)
      promise.then(value => { obj[key] = value })
    } else if (isObject(obj[key]) {
      fetchRefs(obj[key])
    }
  }
}(obj))

await Promise.all(allPromises)