Working with multiple API calls from a Node/Express intermediate API, trying to use promise.all()

Question

I am discovering all kinds of gaps in my understanding during this project. I am working on building an intermediate API server. Some end-points take an array of info, then make an external call for each piece of info, then do some manipulation of the response, and ultimately needs to send a response when everything is done.

I am usually handling a single call at a time, and thought I had a decent grasp of Async Await. I used Promise.all() like three years ago for some parallel calls, but it's been an age, and this doesn't quite translate the same way. I also tried making each step it's on thing and chaining .then()s however some of my functions didn't seen async/ wouldn't trigger a .then(). All the documentation I have looked at has gotten me partway there, but then I am still getting quite stuck.

const createUserDir = async (req, res) =>{
    // make User Directory
    fs.mkdir(path.join(__dirname, `../Users/${req.body.userID}`), { recursive: true },(err)=>{
        if (err) {
            return console.error(err);
        }
        getAllAssetImages(req.body.assets, req.body.config, req.body.userID, res)
    })
}

const getAllAssetImages =async (assets, config, userID, response)=> {
    
    try {
        const allAssets = await Promise.all(
            assets.map(asset => (
// utils.getAsset is an axios call to get a file, this works
                utils.getAsset(asset, config)
                .then(res => fs.mkdir(path.join(__dirname, `../Users/${userID}/${asset.assetId}`),
                ()=>fs.writeFile(path.join(__dirname, `../Users/${userID}/${asset.assetId}/${asset.assetId}.pptx`), res.data, {encoding: 'binary'}, async (err) => {
                    if (err){
                        console.log(err.code)
                    } else {
                        console.log("File written successfully")
//convertPPTS.convertPPTS is an async function that uses ppt-png npm package: works    
                    convertPPTS.convertPPTS([path.join(__dirname,`../Users/${userID}/${asset.assetId}/${asset.assetId}.pptx`)],path.join(__dirname,`../Users/${userID}/${asset.assetId}/`))
                       
                    } 
                }
            ))
        )
            )))
            .then(()=>{
                console.log('please log at the end')
                response.send({status:200, body:'assets available!'})
    })
            console.log('all the promises', allAssets)
        } catch (err){
            throw Error(err)
        }
}

router.post('/', (req,res) => {
     createUserDir(req, res)
     .then(()=>{console.log('all assets written')})
})


export default { router }

It will often finish fetching, writing converting 2 out of three files then say it is done, before it is, then throw an error when it tries to convert a file that isn't there yet.

Answer 1

The biggest thing I did, was remove the mixing of .then() and awaiting promises, leaning into promises and async await. I believe there is room to optimize by allowing some of this to run in parallel, and changing what is being awaited.

const createUserDir = async (req) => {
  let { assets, userID, SP } = req.body;

  fs.mkdir(path.join(__dirname, `../Users/${req.body.userID}`), { recursive: true }, (err) => {
      if (err) {
        console.error(err.message)
        return (err);
      }
    }
  );
  await getAllAssetImages(assets, SP, userID);
};

const getAllAssetImages = async (assets, config, userID) => {
  try {
    await Promise.all(
      assets.map(async (asset) => {
        let res = await showpadUtils.getAsset(asset, config);
        await new Promise((resolve, reject) =>
          fs.mkdir( path.join(__dirname, `../Users/${userID}/${asset.assetId}`), () => (
            fs.writeFile(path.join(__dirname, `../Users/${userID}/${asset.assetId}/${asset.assetId}.pptx`),
                res.data,
                { encoding: "binary" },
                async (err) => {
                  if (err) {
                    console.log(err.code);
                  } else {
                    console.log("File written successfully");
                    resolve(
                      convertPPTS.convertPPTS(
                        [
                          path.join(__dirname, `../Users/${userID}/${asset.assetId}/${asset.assetId}.pptx`),
                        ],
                        path.join(__dirname, `../Users/${userID}/${asset.assetId}/`)
                      )
                    );
                  }
                }
              )
          )
          )
        );
      })
    );

    console.log("please log at the end");
} catch (err) {
    throw Error(err);
}
};

router.post("/", async (req, res) => {
    await createUserDir(req);
    console.log("all assets written");
    res.send({ status: 200, body: "assets available!" });
});