How to create dateadd function in SSJS by calling dateadd in ampscript

Question

I'm trying to create a dateAdd function in SSJS by calling the dateAdd function in Ampscript. The code below works. But I cannot figure out how to make the date argument dynamic. This means the function in my code always starts with the current date time and calculates a new date from there. I would like to make the function truly dynamic by passing a date to the function.

My problem is that the date in SSJS and Ampscript is not formatted in the same way. That is a problem when I pass the date into the ampscript code.

I'm aware of this question (Date manipulation Function SSJS) regarding creating a dateadd function in SSJS, but the answer there takes another approach. It tries to make the dateadd function from scratch in Javascript. I want to take advantage of the function that is already made in Ampscript.

<!-- For debugging only start -->
<p>
  Printing a date in ampscript for comparison<br>
  newDateAmpScript: %%=v(NOW())=%% <br><br>
</p>
<!-- For debugging only end -->


<script runat="server">
  Platform.Load("Core","1.1.1");
  
   // For debugging only start
   var newDateSsjs = new Date();
   Write('Printing a date in Javascript for comparison<br>')
   Write('newDateSsjs: ' + newDateSsjs + "<br><br>");
  // For debugging only end

  function dateAdd(date, intervalNumber, intervalUnit) {
       
   var calulatedDateAmpScriptString = '%' + '%['
                                      + 'VAR @calulatedDate '
                                      + 'SET @calulatedDate = SystemDateToLocalDate(DateAdd(NOW(), ' + intervalNumber +', "' + intervalUnit + '")) '
                                      + 'VAR @calulatedDateIso '
                                      + 'SET @calulatedDateIso = FormatDate(@calulatedDate, "iso") '
                                      + ']%' + '%';
    
      
    // Printing ampscript string for easier debugging
     Write(calulatedDateAmpScriptString + "<br><br>");
     
     try {
       var content = Platform.Function.TreatAsContent(calulatedDateAmpScriptString);
       return Platform.Variable.GetValue("@calulatedDateIso");
     }
     catch(e) {
       Write("error: " + Stringify(e) + "<br><br>")
     }
   }

   // Calling the dateAdd function to test it
   var modifiedDateFrom = dateAdd(newDateSsjs, -18, 'D');
   Write("modifiedDateFrom: " + modifiedDateFrom);
</script>

Answer 1

I would not recommend using SSJS to dynamically create and then run AMPScript like this, it is going to open a TON of risk and slow down processing and load times.

If you just want a dateadd function to reference instead of having to build something new for each need, I can give you a homegrown dateAdd() function I created/Frankensteined in SSJS that you can use. I would not call it perfect and it certainly has some odd coding and such (e.g. each case in switch needs to be filled in order to work right) but it gets the job done.

function dateAdd(date, interval, units) {

  //Backfill of Array.includes
  Array.includes = function(val,arr) {
    for(i=0;i<arr.length;i++){
      if (!r || r == false){r = val == arr[i] ? true: false;}
    }
    return r;
  }

  // Verify if date is a date
  if(!(typeof date.getMonth === 'function'))  
    return 'Not a valid Date';
 
  var ret = new Date(date); //don't change original date

  // Verify if units are positive integers
  if (units < 1) { return 'Unit needs to be an integer of 1 or higher'; }

  // Verify if correct interval || case insensitive
  var arr = ["y","q","m","w","d","h","mi","s","year","quarter","month","week","day","hour","minute","second"]
  if (!(Array.includes(interval.toLowerCase(),arr))) { return 'Incorrect interval passed'; }

  var checkRollover = function() { if(ret.getDate() != date.getDate()) ret.setDate(0);};
  switch(String(interval).toLowerCase()) {
    case 'y'      :  ret = new Date(date.getFullYear() + units, date.getMonth(), date.getDate(), date.getHours(), date.getMinutes(), date.getSeconds(), date.getMilliseconds()); checkRollover();  break;
    case 'year'   :  ret = new Date(date.getFullYear() + units, date.getMonth(), date.getDate(), date.getHours(), date.getMinutes(), date.getSeconds(), date.getMilliseconds()); checkRollover();  break;
    case 'q'      :  ret.setMonth(ret.getMonth() + 3*(units+1)); checkRollover();  break;
    case 'quarter':  ret.setMonth(ret.getMonth() + 3*(units+1)); checkRollover();  break;
    case 'm'      :  ret.setMonth(ret.getMonth() + (units+1)); checkRollover();  break;
    case 'month'  :  ret.setMonth(ret.getMonth() + (units+1)); checkRollover();  break;
    case 'w'      :  ret.setDate(ret.getDate() + 7*units);  break;
    case 'week'   :  ret.setDate(ret.getDate() + 7*units);  break;
    case 'd'      :  ret.setDate(ret.getDate() + units);  break;
    case 'day'    :  ret.setDate(ret.getDate() + units);  break;
    case 'h'      :  ret.setTime(ret.getTime() + units*3600000);  break;
    case 'hour'   :  ret.setTime(ret.getTime() + units*3600000);  break;
    case 'mi'     :  ret.setTime(ret.getTime() + units*60000);  break;
    case 'minute' :  ret.setTime(ret.getTime() + units*60000);  break;
    case 's'      :  ret.setTime(ret.getTime() + units*1000);  break;
    case 'second' :  ret.setTime(ret.getTime() + units*1000);  break;
  }

  return ret;
}

And then just output similar to the AMPScript version:

var date = new Date(),
    interval = 'Q',
    units = 1;
var newDate = dateAdd(date,interval,units);
Write('date: ' + date + '<br>');
Write('interval: ' + interval + '<br>');
Write('units: ' + units + '<br>');
Write('newDate: ' + newDate + '<br>');

Outputs:

date: Fri, 04 Dec 2020 13:28:35 GMT-06:00
interval: Q
units: 1
newDate: Thu, 04 Mar 2021 13:28:35 GMT-06:00

Answer 2

Here is one way to do this using the AMPscript DateAdd() function by invoking it with SSJS. I also included the AMPscript date format as a parameter, so that can be changed to match your desired format.

<script runat="server">
Platform.Load("Core","1.1.1") // load platform library

//call the dateaddJS function, passing the startingDate, intervalNumber, intervalUnit, and desired format all as separate arguments
var startingDate = "12/19/2020"
var modifiedDate = dateAddJS(startingDate, -18, 'D', "mm/dd/yyyy") 

//output startingDate
Write("<hr>startingDate: " + startingDate)
//output date calculated by ampscript dateadd function
Write("<hr>modifiedDate: " + modifiedDate)

function dateAddJS(date, intervalNumber, intervalUnit, dateFormat) {
    var date = new Date(date)
    // pass our js variables to ampscript variables
    Variable.SetValue("date",date)
    Variable.SetValue("intervalNumber",intervalNumber)
    Variable.SetValue("intervalUnit",intervalUnit)
    Variable.SetValue("dateFormat",dateFormat)
    // return ampscript forced to run by SSJS TreatAsContent function 
    return TreatAsContent("%%[output(formatdate(dateadd(@date,@intervalNumber,@intervalUnit),@dateFormat))]%%")
}
</script>