By using the JavaScript transform, you can add the current date stamp to your data set.

For example, this is the data we have in one JSON feed:

To add a new column containing the current date stamp, we are going to create a JavaScript transform off of this feed.

In the Script tab of the JavaScript transform, we are going to enter the following code:

function getAttributes(sourceAttrs, nodeVars, secVars, sourceRecords) {
  var attributes = [];
  sourceAttrs.forEach(function(attrList) {
    attrList.forEach(function(attr) {
      attributes.push(attr);
    });
  });
  // Adding new attribute to display current date
  var sampleAttr = {
    name : 'dateNow', // Alphanumerics and underscores only; no leading, trailing, or adjacent underscores
    type : 'date', // 'string'|'int'|'long'|'number'|'boolean'|'date'
    isId : false, // true|false
    units : null, // 'millis'|'seconds' (if attribute is timestamp)
    format : 'yyyy.mm.dd' // string consisting of valid Java SimpleDateFormat pattern
  };
  attributes.push(sampleAttr);
  return jsAttributesSuccess(attributes, "Example Success");
}
function getRecords(sourceRecords, nodeVars, secVars, attributes) {
  var records = [];
  var currentdate = new Date(); 
var datetime = "Last Sync: " + currentdate.getDate() + "/"+ (currentdate.getMonth()+1)  + "/" + currentdate.getFullYear() + " @ "  + currentdate.getHours() + ":"  + currentdate.getMinutes() + ":" + currentdate.getSeconds();
  sourceRecords.forEach(function(recordList) {
    recordList.forEach(function(record) {
      record.dateNow = datetime; //Assigning current date stamp to previously made attribute
      records.push(record);
    });
  });
  return jsRecordsSuccess(records, "Example Success");
}

In the Preview, a new column with the current date (dateNow) will be displayed: