dataTransferItemToArrayBuffer.js

function dataTransferItemToArrayBuffer(dataTransferItem){
  return new Promise((resolve, reject) => {
  if(dataTransferItem.kind !== 'file') {return reject(new Error('DataTransferItem is not of kind "file"'));}
  const file = dataTransferItem.getAsFile();
  
  var reader = new FileReader();
  reader.onload = function() {

    var arrayBuffer = this.result,
      array = new Uint8Array(arrayBuffer);

    resolve(arrayBuffer);

  }
    reader.onerror = reject;
  reader.readAsArrayBuffer(file);
  });
}