empty-s3-buckets.js

const bb = require('bluebird');
const AWS = require('aws-sdk');

const s3 = new AWS.S3();

const removeObject = (bucketName, obj) => {
  const params = {
    Bucket: bucketName,
    Key: obj.Key,
  };
  return s3.deleteObject(params).promise();
};

const emptyBucket = bb.coroutine(function* empty(bucketName) {
  const data = yield s3.listObjects({ Bucket: bucketName }).promise();
  const tasks = data.Contents.map(obj => removeObject(bucketName, obj));
  yield Promise.all(tasks);
});

emptyBucket(process.env.BUCKET_ONE)
  .then(() => emptyBucket(process.env.BUCKET_TWO))
  .then(() => emptyBucket(process.env.BUCKET_THREE))
  .then(() => { /* do something */ })
  .catch(err => console.log(err));

// or

Promise.all([
  emptyBucket(process.env.BUCKET_ONE),
  emptyBucket(process.env.BUCKET_TWO),
  emptyBucket(process.env.BUCKET_THREE)])
  .then(() => { /* do something */ })
  .catch(err => console.log(err));