s3.js

const AWS = require('aws-sdk')

// a function that returns a promise
function copyFileToS3() {
  
  // initialise AWS S3
  const s3 = new AWS.S3({
    accessKeyId: 'whatever',
    secretAccessKey: 'whatever',
    endpoint: 'http://localhost:4566', // localstack is running on port 4566. Imagine this was the real S3 endpoint
    s3ForcePathStyle: true,
  })
  
  const copyObjectParams = {
    Bucket: 'some-bucket',
    CopySource: 'some-bucket/some/path/myfile.json,
    Key: 'some-bucket/some/other/path/myfile.json',
  }
  
  return s3.copyObject(copyObjectParams).promise()
}