Google Sheets Script is a great tool that automates menial work on your spreadsheet. However, you might encounter a common issue where a script triggers twice, leading to duplicate actions and unexpected results. This can be frustrating but there’s no need to panic. Let's dive into the common causes and solutions for this issue.

How Google Sheets Script Works

Before we start troubleshooting, it's essential that we understand how triggers work in Google Sheets. Triggers are events that automatically execute your script. There are two main types here:

1. Simple Triggers: These include onEdit, onOpen, and onInstall, which do not require special authorization. They are easy to set up but have limitations, such as restricted service access.
2. Installable Triggers: These include time-driven and form-submit triggers requiring user authorization. They offer more functionality and can access services that are not available for simple triggers.

Common Causes of Double Triggering

There are usually only five reasons why your script triggers twice. Try going over these four basic troubleshooting steps to see if you can fix the issue:

1. Multiple Triggers Set

One of the most common reasons a script might trigger twice is that multiple triggers have been set up for the same function. This can happen when you have both a simple and an installable trigger set for the same script.

Solution:

• Check the triggers set up for your script by going to Extensions > Apps Script > Triggers.
• Remove any duplicate triggers that may be causing the script to run twice.

2. Redundant Code Execution

Sometimes, the script logic itself can lead to redundant execution. For instance, if a script modifies the sheet that it's listening to for changes, it might trigger itself again.

Solution:

• Make sure your script is not making unnecessary changes that could lead to re-triggering.
• Use conditional statements to prevent the script from making changes unless absolutely necessary.

3. Spreadsheet Settings

Another possible cause of double triggering is spreadsheet settings, particularly when working with shared sheets. Changes made by collaborators might unexpectedly trigger your script.

Solution:

• Review your sharing settings and ensure that triggers are set up correctly for shared access.
• Consider limiting triggers to specific users if appropriate.

4. Form Submissions

If your script is tied to form submissions, each form submission can trigger the script multiple times if not correctly configured.

Solution:

• Check the form submission handling code to ensure each submission is processed only once.
• Consider adding a timestamp or unique identifier check to prevent duplicate processing.

5. Script Execution Timeouts

If your script takes a long time to run, it might be interrupted and restarted automatically. This can sometimes lead to the script running twice.

Solution:

• Optimize your script's performance to reduce execution time.
• Consider breaking down long-running scripts into smaller functions.
• Implement error handling and retry logic to handle interruptions gracefully.

How to Debug Your Google Sheets Script

Here’s the tricky part. Every developer or programmer knows debugging is the most tedious and head scratching process. Thankfully, Google Sheets have made it easy to identify issues if they arise. Here are some steps to help you debug:

1. Review Recent Changes

This might be the most obvious “debugging” step but in some cases, the simplest solution is often the best one. If your script was working correctly before, review any recent changes to the script or the spreadsheet setup that could have introduced new bugs or conflicts.

• Version History: Use the Google Apps Script version history to revert to a previous version and identify when the issue started.
• Change Log: Maintain a change log to track modifications and their impact on the script’s behavior.

2. Log Output with Detailed Information

Make logging easier by including detailed information about the script’s execution. Use Logger.log() strategically to output variable values, function entry and exit points, and other critical data. Doing it this way can potentially help you pinpoint exactly when and where your script is triggering multiple times.

function onEdit(e) {

  Logger.log("Script triggered onEdit: %s", new Date());

  Logger.log("Edited range: %s", e.range.getA1Notation());

  Logger.log("Old value: %s", e.oldValue);

  Logger.log("New value: %s", e.value);

}

3. Use Breakpoints and the Debugger

The Google Apps Script editor includes a built-in debugger that allows you to set breakpoints and step through your code line by line.

• Set Breakpoints: Click on the line number where you want to pause execution. This lets you inspect the state of your variables and understand the flow of the script.
• Step Through Code: Use the debugger to execute your script one line at a time, allowing you to observe changes and identify unexpected behavior.

4. Implement Conditional Logging

Use conditional logging to output messages only when certain conditions are met. This helps you focus on specific scenarios that might lead to double triggering. This technique helps reduce log clutter and highlights the critical paths in your code:

function onEdit(e) {

  if (e.value === "trigger condition") {

    Logger.log("Condition met, value: %s", e.value);

  }

}

5. Monitor Script Execution Time

Scripts that execute for too long can sometimes restart or be interrupted, leading to unexpected results. Monitor the execution time and optimize your code to ensure it runs efficiently.

• Optimize Loops: Minimize operations within loops to improve performance.
• Batch Operations: Use batch operations like getValues() and setValues() to process data more efficiently.

6. Check for Hidden Dependencies

Make sure your script does not have hidden dependencies that can trigger multiple times like:

• Linked Cells: Ensure that changes in one cell aren’t inadvertently affecting another, leading to additional triggers.
• External Data: Check for scripts dependent on data from external sources that might update more frequently than expected.

7. Use Temporary Flags

Implement temporary flags or markers in your spreadsheet to track whether certain parts of your script have already been executed. This can prevent double execution by providing checkpoints.

function onEdit(e) {

  var sheet = e.source.getSheetByName("Sheet1");

  var flagCell = sheet.getRange("A1");

  if (flagCell.getValue() === "executed") {

    return; // Exit if already executed

  }

  // Script logic here

  flagCell.setValue("executed");

}

8. Test with Simulated Triggers

Simulate different trigger conditions to see how your script responds. This can help you identify edge cases that might cause double triggering.

• Use Test Data: Create test scenarios that mimic real-world conditions.
• Evaluate Responses: Assess how your script handles these conditions and make necessary adjustments.

Conclusion

Running into issues where your Google Sheets script triggers twice can be frustrating, but with a solid understanding of triggers and some strategic debugging, you can quickly get things back on track. Remember to carefully check for multiple triggers, refine your script logic to avoid unnecessary re-execution, and use the debugging tools available to pinpoint the exact cause. It might be difficult at first but that’s part of the process; you got this!

Looking to sharpen your skills even further? Explore the training courses at Intellezy, where you can dive deep into Google Sheets, scripting, and more to enhance your professional capabilities. Request a free trial for you and your accounting team today!