Is it possible to translate ANY async-await function to old school .then().catch() when loop is involved

Question

I am trying to convert my async-await function to the old school Promises way.

The main challenge is that I need to loop through a function and use the response to fetch more.

Here is my function:

async function getHierarchyForId(id) {
   try {
      let result = '';
      let member = await fetchMemberById(id)
      let tmp = member.parentMemberId
      console.log(member)
      for(let i = member.level; i > 1; i--){
         let parent = await fetchMemberById(tmp)
         console.log(parent)
         if(i == 2){
            result += `${parent.name}`
         }else{
            result += `${parent.name} -> `
         }
         tmp = parent.parentMemberId
      }
      console.log(result)
      return result
   }catch(e){
      console.log(e)
   }
}

This is correctly working, and I try to translate that to a promise function.

Here is what I got, but some wrong code is written.

async function getHierarchyForId(id) {
   fetchMemberById(id)
      .then(member => {
         let result = '';
         let tmp = member.parentMemberId
         for (let i = member.level; i > 1; i--) {
            let parent = fetchMemberById(tmp)
               .then(r => {
                  console.log(r)
                  if (i == 2) {
                     result += `${r.name}`
                  } else {
                     result += `${r.name} -> `
                  }
                  tmp = parent.parentMemberId
               })
               .catch(err => console.log(err))
         }
         console.log(result)
         return result
      })
      .catch(e => console.log(e))
}

Thank you for your time !

async-await *is* promises. did you mean converting an inclined handler to a callback? **why would you want this?** — 0xLogN, Mar 24 '22 at 13:39
yes, i meant translate await to then.catch . It's an exercise I need to do — Yoël Zerbib, Mar 24 '22 at 13:41
I read that, but I know how to do X. It's the Y that I'm struggling to undertand, even though I am close to the answer — Yoël Zerbib, Mar 24 '22 at 13:42
You can return `new Promise(resolve => ...)` and call `resolve` whenever your data is ready to handle multiple await/callbacks/then. — Almaju, Mar 24 '22 at 14:41

score 1 · Accepted Answer · answered Mar 24 '22 at 14:09

Yes, any async/await code can be translated to then/catch code.

For your case you'll need to make an "asynchronous loop": create a function that gets the first promise, and then as a then callback action, (later) calls that new function again, so chaining promises until the final result is known, at which point all those promises resolve.

function getHierarchyForId(id) {
   return fetchMemberById(id).then(member => {
      console.log(member);
      return (function loop(id, i, arr) {
          if (i <= 1) return arr.join(" -> "); // loop done
          return fetchMemberById(id).then(parent => {
             console.log(parent);
             return loop(parent.parentMemberId, i-1, arr.concat(parent.name));
          });
      })(member.parentMemberId, member.level, []); // Start of the loop
   }).catch(e => {
      console.log(e)
   });
}

Is it possible to translate ANY async-await function to old school .then().catch() when loop is involved

1 Answers1