Lambda function to get storage cost for the S3 Bucket Folder

handler.js

const AWS = require('aws-sdk');
const s3 = new AWS.S3();

let totalObjects = 0;
let dataMap = {};

const formatBytes = (bytes) => {
    const marker = 1024;
    const gigaBytes = marker * marker * marker;
    const decimal = 2; 
    return (bytes / gigaBytes).toFixed(decimal);
}

// Prices are based on the AWS Documentation
const s3Pricing = {
    "STANDARD": 0.025,
    "INTELLIGENT_TIERING": 0.025,
    "GLACIER_Flexible_Retrieval": 0.0045,
    "GLACIER": 0.0045
}

function getObjects({ bucket, folder, marker, prev }, callback) {
  var params = {
    Bucket: bucket,
    Marker: marker,
    Prefix: folder,
  }

  return s3.listObjects(params).promise().then(data => {
    let objects = data.Contents;
    totalObjects += objects.length;
    
    objects.map(e => {
        if (!dataMap[e.StorageClass]) {
            dataMap[e.StorageClass] = { count: 0, size: 0 }
        }
        if (e.Size > 0) {
            dataMap[e.StorageClass].count += 1
            dataMap[e.StorageClass].size += e.Size
        }
    })
    Object.keys(dataMap).map(k => {
        dataMap[k].gbSize = formatBytes(dataMap[k].size)
        dataMap[k].price = `${(parseFloat(dataMap[k].gbSize) * s3Pricing[k]).toFixed(2)} USD`;
    })
    
    if(data.IsTruncated){
      const length = data.Contents.length;
      const marker = data.Contents[length - 1].Key;
      return getObjects({ bucket, folder, marker, prev: objects});
    }
    
    return objects;
  });
}

exports.handler = async (event) => {
    totalObjects = 0;
    dataMap = {};
    
    await getObjects({
      bucket: event.bucket,
      folder: event.folder
    })

    let res =  {
      bucket: event.bucket,
      folder: event.folder,
      totalObjects,
      cost: {
        ...dataMap
      } 
    };
    
    console.log(res);    
    return res;
};