S3 download promise: nodeJS promise to download file from amazon S3 to local destination

s3download_promise.js

const AWS = require('aws-sdk');
const fs = require('fs')

const s3download = (bucketName, keyName, localDest) => {

    if (typeof localDest == 'undefined') {
        localDest = keyName;
    }

    let params = {
        Bucket: bucketName,
        Key: keyName
    }

    let file = fs.createWriteStream(localDest)

    return new Promise((resolve, reject) => {
        s3.getObject(params).createReadStream()
        .on('end', () => {
            return resolve();
        })
        .on('error', (error) => {
            return reject(error);
        }).pipe(file)
    });
};

Same code but did some minor cleanups and adds missing import. @milesrichardson

var AWS = require('aws-sdk');
const fs = require('fs');

var s3 = new AWS.S3();

const s3download = (bucketName, keyName, localDest) => {

    if (typeof localDest == 'undefined') {
        localDest = keyName;
    }

    let params = {
        Bucket: bucketName,
        Key: keyName
    };

    let file = fs.createWriteStream(localDest);

    return new Promise((resolve, reject) => {
        s3.getObject(params).createReadStream()
        .on('end', () => {
            return resolve();
        })
        .on('error', (error) => {
            return reject(error);
        }).pipe(file);
    });
};

A naive question: Why the resolve and reject is on read stream but not write stream? Thanks!