How to use postProcess in tabletop.js?

Good afternoon everyone

I am importing data from a Google Spreadsheet as JavaScript objects but I cannot seem to be able to use postProcess option to modify the data after it has been processed by tabletop.js.

This is the example I have taken from GitHub (please note I am still a beginner). I have replace the names after element["___"] with the names of my columns and it won’t do anything.

postProcess: function(element) {
   // Combine first and last name into a new column
   element["full_name"] = element["first_name"] + " " + element["last_name"];

   // Convert string date into Date date
   element["timestamp"] = Date.parse(element["displaydate"]);

I have tried to replace function(element) with function(data). This is the rest of my code:

var publicSpreadsheetUrl = '';

  function init() {
    Tabletop.init( { key: publicSpreadsheetUrl,
                     callback: showInfo,
                     parseNumbers: true,
                     postProcess: function(element) {
                     element["timestamp"] = element["day"] + " " + element["hour"]

  function showInfo(data, tabletop) {

  window.addEventListener('DOMContentLoaded', init);

So far no matter what I put in postProcess: function doesn’t seem to work.

Many thanks for your help.