Asynchronous call inside a javascript for loop

Question

I need to create file for each month, before next step of logic, but when I creating it inside for loop, it does not wait untill finish of this operation.

I tried to take for loop into separate async method, which I call inside main deleteAvatars method with "await".

private async s3ListsCreator(mainPathPart: string, type: string) {
    const promises = Constants.MONTHS_FOLDERS.map(async folder => {
      const s3Files: string[] = await this.getAllFiles(type, folder);
      try {
        await this.uploadS3FilesList(mainPathPart, s3Files, folder);
      } catch (err) {
        this.logger.error(err);
        return this.response
          .addError(new HttpErrors[400](`Upload on s3 list is unsuccessful`))
          .build();
      }
    });
    await Promise.all(promises);
}
 async deleteAvatars(): Promise<Response> {
try {
      await this.s3ListsCreator(fixPathPart, Constants.SUBFOLDERS.avatars);
    } catch (err) {
      this.logger.error(err);
      return this.response
        .addError(new HttpErrors[400](`Upload on s3 list is unsuccessful`))
        .build();
    }
try {
      await this.filesCleanUpLambdaCall(
        Constants.LIST_NAMES.avatarsList,
        avatarResolutions,
        Constants.SUBFOLDERS.avatars.concat(Constants.IMAGE, '/'),
      );
    } catch (err) {
      this.logger.error(err);
      return this.response
        .addError(new HttpErrors[400](`Clean up is unsuccessful`))
        .build();
    }
}

I need to create all files before lambda call, but I create random number of files before I call lambda function.

logs:

NB-010: https://s3.com/avatars/image/01/s3list.txt
NB-010: https://s3.com/avatars/image/02/s3list.txt
NB-010: https://s3.com/avatars/image/03/s3list.txt
NB-010: https://s3.com/avatars/image/04/s3list.txt
NB-010: https://s3.com/avatars/image/05/s3list.txt
NB-010: https://s3.com/avatars/image/06/s3list.txt
NB-010: https://s3.com/avatars/image/07/s3list.txt
NB-010: https://s3.com/avatars/image/08/s3list.txt
NB-010: https://s3.com/avatars/image/09/s3list.txt
NB-010: https://s3.com/avatars/image/10/s3list.txt
NB-010: lambda input:{"FunctionName":"filesCleanUp","Payload":"{\"listName\":\"avatars.txt\"}"}
NB-010: https://s3.com/avatars/image/11/s3list.txt
NB-010: https://s3.com/avatars/image/12/s3list.txt

I'm sorry that I don't have time to give a proper answer right now, but you should look into Promise.all — Dov Rine
– Dov Rine, Commented Oct 15, 2019 at 11:09

M.Amer · Accepted Answer · 2019-10-15 11:19:32Z

1

if you convert the for loop into map then you can use Promise.all to solve that

const promises = array.map(delayedLog);
// wait until all promises are resolved
await Promise.all(promises);

answered Oct 15, 2019 at 11:19

M.Amer

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