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Best answer

Custom Javascript adding months to datetime incorrectly

  • March 28, 2025
  • 6 replies
  • 43 views
Z

I’ve been trying to add a custom action to a Zap (and then to do the same with custom code) and seem to be having an issue with dates/datetimes. I am simply attempting to add 12 months to a specific date in Javascript. My code works in *every other interface* that I test it in, but for some reason, the same code returns inaccurate outputs when I use Zapier custom code or custom actions. Code is here: 

 

const numMonths = 12;
const unixStartDate = 1743179322; //March 28th, 2025 in unix - set dynamically in the eventual action

const startDate = new Date(unixStartDate * 1000); //Convert unix to datetime
console.log('Start Date ::: '+startDate);

const newEndDate = new Date(startDate.setMonth(startDate.getMonth() + numMonths)); //Add 12 months
console.log('End Date ::: '+newEndDate); //Would expect March 28th, 2026

 

This code runs correctly on other interfaces, but when I run it in Zapier, it returns the date Fri Sep 19 2042 -- 18 years ahead. I can find no other reasonable solution other than something is wrong on Zapier's side. Any help would be appreciated.

Best answer by Troy Tessalone

​@zgoldberg 

NOTES:

  • Formatter steps count as 0 Tasks in Zap Runs
  • Codes steps count as 1 Task in Zap Runs

With the help of ChatGPT I got this to JavaScript Code to work:

const numMonths = 12;
const unixStartDate = inputData.UNIX;

const startDate = new Date(unixStartDate * 1000); // Convert UNIX to Date
const newEndDate = new Date(startDate); // Clone to avoid mutating
newEndDate.setMonth(newEndDate.getMonth() + numMonths); // Add 12 months

// Format output
const formattedStartDate = startDate.toISOString();
const formattedEndDate = newEndDate.toISOString();

const startUnix = Math.floor(startDate.getTime() / 1000);
const endUnix = Math.floor(newEndDate.getTime() / 1000);

return {
  dates: {
    start: formattedStartDate,
    end: formattedEndDate
  },
  unix: {
    start: startUnix,
    end: endUnix
  }
};

 

OUTPUT

 

This post has been closed for comments. Please create a new post if you need help or have a question about this topic.

6 replies

Troy Tessalone
Zapier Orchestrator & Solution Partner
Forum|alt.badge.img+14
  • Troy TessaloneZapier Orchestrator & Solution Partner
  • Zapier Orchestrator & Solution Partner
  • 34081 replies
  • March 28, 2025

Hi ​@zgoldberg 
Why not use this Zap action: Formatter > Date/Time > Add/Subtract Time

Formatter help: https://zapier.com/apps/formatter/integrations#help

 

TIP: Try asking ChatGPT to help you troubleshoot and optimize the Code.

⚡ Troy Tessalone - AutomationAce.com | Platinum Authorized Zapier Solution Partner | #1 Zapier Community Contributor
Z
  • zgoldbergBeginner
  • Author
  • Beginner
  • 3 replies
  • March 28, 2025

Thanks for the tip about the formatter, ​@Troy Tessalone, that could be a temporary solution. However, now I’m using 3 actions (transform the Unix code to a datetime >  add the months > convert back to Unix) where I should be able to do this all in a single code block.

Again, the code - as far as I can tell - is not the issue. I have successfully used it in a number of other interfaces. I’m wondering why it’s only causing this issue in Zapier and not elsewhere. 

Troy Tessalone
Zapier Orchestrator & Solution Partner
Forum|alt.badge.img+14
  • Troy TessaloneZapier Orchestrator & Solution Partner
  • Zapier Orchestrator & Solution Partner
  • 34081 replies
  • Answer
  • March 28, 2025

​@zgoldberg 

NOTES:

  • Formatter steps count as 0 Tasks in Zap Runs
  • Codes steps count as 1 Task in Zap Runs

With the help of ChatGPT I got this to JavaScript Code to work:

const numMonths = 12;
const unixStartDate = inputData.UNIX;

const startDate = new Date(unixStartDate * 1000); // Convert UNIX to Date
const newEndDate = new Date(startDate); // Clone to avoid mutating
newEndDate.setMonth(newEndDate.getMonth() + numMonths); // Add 12 months

// Format output
const formattedStartDate = startDate.toISOString();
const formattedEndDate = newEndDate.toISOString();

const startUnix = Math.floor(startDate.getTime() / 1000);
const endUnix = Math.floor(newEndDate.getTime() / 1000);

return {
  dates: {
    start: formattedStartDate,
    end: formattedEndDate
  },
  unix: {
    start: startUnix,
    end: endUnix
  }
};

 

OUTPUT

 

⚡ Troy Tessalone - AutomationAce.com | Platinum Authorized Zapier Solution Partner | #1 Zapier Community Contributor
JammerS
Forum|alt.badge.img+6
  • JammerSZapier Staff
  • Zapier Staff
  • 3527 replies
  • March 31, 2025

Hi ​@zgoldberg,
 
We just wanted to see how everything is going with your Zap. Did Troy's recommendation get the job done? Feel free to reach out if you need further assistance with your Zap. We're glad to address any concerns and assist you.
 
We're looking forward to your response.

Z
  • zgoldbergBeginner
  • Author
  • Beginner
  • 3 replies
  • April 1, 2025

Thanks so much ​@Troy Tessalone that does work, though honestly I’m not sure why. I have the following code in a custom action:

// Calculate the new end date using DateTime values
  const startDate = new Date(subscription.current_period_start * 1000); // Convert Unix timestamp to milliseconds
  console.log('StartDate in Unix ::: '+subscription.current_period_start);
  console.log('MONTHS ::: '+months);
  console.log('FORMATTED START DATE ::: '+startDate);
  const newEndDate = new Date(startDate);
  newEndDate.setMonth(newEndDate.getMonth()+months);
  console.log('OG VALUE OF NEW ENDDATE ::: '+newEndDate);

  // Convert the new end date to a Unix timestamp
  const newEndDateUnix = Math.floor(newEndDate.getTime() / 1000);
  console.log('EndDate in Unix ::: '+newEndDateUnix);

And I end up with the following log:

StartDate in Unix ::: 1743194789

MONTHS ::: 12

FORMATTED START DATE ::: Fri Mar 28 2025 20:46:29 GMT+0000 (Coordinated Universal Time)

OG VALUE OF NEW ENDDATE ::: Sun Sep 28 2042 20:46:29 GMT+0000 (Coordinated Universal Time)

EndDate in Unix ::: 2295549989

I can’t for the life of my understand why it’s calculating this way. Again- this is only on the custom action. Using a Code by Zapier action, it seems to be fine. Not sure if I’m still missing something or if something is wrong with the action itself. Regardless, I appreciate it! 

JammerS
Forum|alt.badge.img+6
  • JammerSZapier Staff
  • Zapier Staff
  • 3527 replies
  • April 2, 2025

Thank you for confirming that Troy’s resolution got the Zap running. This will significantly help our Community members to have as a reference for the same issue.

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