code written for Comma Chameleon in electron JS - inexplicable persistence of data

datapackage.js

var exportdata = function() {
  var window = BrowserWindow.getFocusedWindow();

  datapackage = new BrowserWindow({width: 450, height: 600, 'always-on-top': true});
  datapackage.loadUrl('file://' + __dirname + '/../comma-chameleon/views/datapackage.html');

  datapackage.on('closed', function() {
    datapackage = null;
  });

  //there follows some horrible async
  //my understanding of why async is as follows - we have no controllers / model structure to control the data mgmt
  //ergo to ensure we are getting the right data for the correct CSV we are reliant on the Browser.getFocusedWindow() method
  //at two points in this long method it is necessary to ensure that this is the intended window, when the header row data is sought
  //and when the CSV to be saved to the package is retrieved by the dialog module



  ipc.once('sendDatapackage', function(e, data, includeHeaders) {
    // data here is the object generated by filling out the form, e is event param generated by using IPC
    //console.log("at begin of function this is data "+JSON.stringify(data,null, 2));
    var currentFileName = window.getTitle();
    var suggestedFileName = path.basename(currentFileName).replace('.csv', '');

    var thatData = data;
    // writing this assignment because the logic of the closure below reminds me of 'this' and 'that'

    // issue calls to get the JSON rendering of the header row
    if(includeHeaders === "true"){
      window.webContents.send('schemaFromHeaders');
      ipc.on('jsonHeaders', function(event, json){
        //assign the headers to the JSON datapackage
        datapackageJson(thatData, json);
        //console.log("currently executing within the IPC function that retrieves the headers");
        //thatData["fields"] = json["fields"];
        //return data;
      });
    } else {
      datapackageJson(thatData);
      //return data;
    }
    //console.log("this is the data immediately after the includeHeaders conditional "+JSON.stringify(data));
    //var data = datapackageJson(data);

    Dialog.showSaveDialog({
      defaultPath: suggestedFileName+".zip",
      //defaultPath: includeHeaders,
      filters: [
        { name: 'text', extensions: ['zip'] }
      ],
      //defaultPath: 'datapackage.zip'
    }, function (fileName) {
      if (fileName === undefined) return;
      datapackage.close();
      window.webContents.send('getCSV');

      ipc.once('sendCSV', function(e, csv) {
        //console.log("this is the point right before zipping up data has not be reassigned ONCE: data - "+JSON.stringify(data,null, 2));
        generateDatapackage(fileName, data, csv)
      });
    });
  });

  ipc.once('datapackageCanceled', function() {
    datapackage.close();
  });
}

function datapackageJson(data_arg, headers) {
  //console.log(data);
  data_arg.keywords = data_arg.keywords.split(",");
  //console.log(data.keywords);
  data_arg.resources = [
    {
      "name": data_arg.name,
      "path": "data/" + data_arg.name + ".csv",
      "mediatype": "text/csv",
      "schema": headers
    }
  ]
  return data_arg
}

function generateDatapackage(fileName, data_arg, csv) {
  // this function is only triggered after the user confirms the name of what they wish to save the package as
  //console.log("within async triggered generate data package function "+data_arg);
  zip = new require('node-zip')();
  zip.file('datapackage.json', JSON.stringify(data_arg,null, 2));
  zip.file('data/' + data_arg.name + '.csv', csv);
  zipData = zip.generate({base64:false,compression:'DEFLATE'});
  Fs.writeFileSync(fileName, zipData, 'binary');
}

something very weird exists in this file, must be something to do with closure but I am at a loss as to how the data passed in at line 28 persists the changes that are made to a variable thatData by functions on line 42 and 48 because data passed in line 68 has all those changes persisted

var thatData = data; actually creates a pointer to the same object, so any methods that transform 'thatData' also apply to data, consequence of Javascripts pass-by-value / pass-by-reference