Sequential API calls, do I use Promise.all or an iterative function?

Question

Taking an input array of IDs, on each item I have to sequentially execute a fetch request, and then perform a database operation using the returned results.

IDs = [1,2,3,4]

I have two options for this,

Using Promise.all, I perform all of the fetch calls up front and push the results to an array. Then, once all the calls have been made, i take this resulting array and loop through it to perform my DB operation on each result.

let requests = ids.map(id => {
   return new Promise((resolve, reject) => {
      request({
         uri: <API url>+‘?id=' + id,
         method: ‘GET’
      },
      (err, res, body) => {
      if (err) { reject(err) }
      resolve(body)
      })
   })
})
Promise.all(requests).then((body) => { 
   body.forEach(res => {
   if (res)
      productsToReturn.push(JSON.parse(res).productInfo)
   })
}).catch(err => console.log(err))

Using a reducer that performs the fetch call and the database operation on each ID before moving onto the next.

    return files.reduce((chain,currentFile) => {
            return chain.then(_ => download(currentFile));
                },Promise.resolve())
                }
reductiveDownloadChain(mockFiles)

Is one of these methods a better choice? How do I know which to pick?

Calling `request` in a `map` callback doesn't make anything sequential. — Bergi, Jan 16 '21 at 22:19
Instead of `reduce`, use modern `async`/`await` where you can just wait in a loop. — Bergi, Jan 16 '21 at 22:19
just use `await` inside for loop in the context of an async function — Dmitriy Mozgovoy, Jan 16 '21 at 22:29
@user3869231 [You can't use `forEach` with `async` functions](https://stackoverflow.com/a/37576787/1048572) — Bergi, Jan 16 '21 at 22:40
Gah I think i just wasted 6 hours on debugging async in forEach loop. Thank you — user3869231, Jan 16 '21 at 22:43

Sequential API calls, do I use Promise.all or an iterative function?

0 Answers0