Triggers (onEdit, onOpen) in Google Sheets - Step-by-Step Guide

Introduction

Triggers in Google Sheets let you run a script automatically when you open a sheet or edit a cell. This helps you automate tasks without clicking buttons.

When you want to show a welcome message every time someone opens the sheet

When you want to check data or update values automatically after a user changes a cell

When you want to log changes made to the sheet without manual effort

When you want to send notifications after edits happen

When you want to prepare or reset the sheet layout each time it opens

Steps

Step 1: Open

- Google Sheets file

Your spreadsheet is visible and ready

Step 2: Click

- Extensions menu > Apps Script

The Apps Script editor opens in a new tab

Step 3: Type

- Code editor

You enter a function named onOpen or onEdit

💡 Use exact function names: onOpen() or onEdit(e) for automatic triggers

Step 4: Write

- Inside the function

Your script runs automatically when the event happens

💡 For example, onOpen runs when the sheet opens; onEdit runs after any cell edit

Step 5: Save

- Apps Script editor (File > Save or Ctrl+S)

Your script is saved and ready to run

Step 6: Return

- Google Sheets tab

Your script triggers will run automatically on open or edit

Before vs After

Before

No script runs automatically when opening or editing the sheet

After

A welcome message appears on open or a cell value updates automatically after editing

Settings Reference

Simple Triggers

📍 Apps Script editor, function names onOpen() and onEdit(e)

Run code automatically when the sheet opens or a cell is edited

Default: No triggers run until you add these functions

Installable Triggers

📍 Apps Script editor > Triggers (clock icon) > Add Trigger

Create triggers with more permissions and options than simple triggers

Default: No triggers installed by default

Common Mistakes

Naming the function something other than onOpen or onEdit

Simple triggers only run if the function name is exactly onOpen or onEdit

Use the exact function names onOpen() or onEdit(e) for automatic triggers

Expecting onEdit to run without the event object parameter

onEdit needs the event object (e) to know what was edited

Define onEdit with a parameter like onEdit(e) to access edit details

Trying to run scripts that require authorization inside simple triggers

Simple triggers have limited permissions and cannot perform some actions

Use installable triggers from the Triggers menu for scripts needing more permissions

Summary

Triggers run scripts automatically when you open or edit a Google Sheet

Use onOpen() to run code on sheet open and onEdit(e) to run code after edits

Simple triggers have limits; use installable triggers for advanced needs

Practice

1. What does the onOpen trigger do in Google Sheets?

easy

A. Saves the spreadsheet automatically

B. Runs a script automatically when the spreadsheet is opened

C. Runs a script when a cell is edited

D. Deletes all data when the sheet is opened

Solution

1. Step 1: Understand the purpose of onOpen

   The onOpen trigger runs a script automatically when the spreadsheet is opened by a user.

2. Step 2: Compare with other triggers

   Unlike onEdit, which runs on cell changes, onOpen activates only on opening the file.

3. Final Answer:

   Runs a script automatically when the spreadsheet is opened -> Option B

4. Quick Check:

   onOpen = runs on open [OK]

Hint: Remember: onOpen triggers when file opens, not on edits [OK]

Common Mistakes:

• Confusing onOpen with onEdit trigger
• Thinking onOpen runs on every cell change
• Assuming onOpen saves the file automatically

2. Which of the following is the correct way to define an onEdit trigger function in Google Sheets Apps Script?

easy

A. function onEdit(e) { /* code here */ }

B. function onEdit { /* code here */ }

C. function onEdit() { /* code here */ }

D. function onEdit(e) => { /* code here */ }

Solution

1. Step 1: Recall correct function syntax with event object

   The onEdit trigger function must accept an event object parameter e to access edit details.

2. Step 2: Check syntax correctness

   function onEdit(e) { /* code here */ } uses correct function declaration with parameter e and braces.

3. Final Answer:

   function onEdit(e) { /* code here */ } -> Option A

4. Quick Check:

   onEdit needs (e) parameter and braces [OK]

Hint: Include (e) parameter to access edit info in onEdit [OK]

Common Mistakes:

• Omitting the (e) parameter in onEdit function
• Using arrow function syntax which is invalid here
• Missing parentheses or braces in function declaration

3. Given this onEdit function in Google Sheets Apps Script:

function onEdit(e) {
  if (e.range.getA1Notation() === 'A1') {
    e.source.getActiveSheet().getRange('B1').setValue('Edited!');
  }
}

What happens when you edit cell A1?

medium

A. Nothing happens

B. Cell A1 will be cleared

C. Cell B1 will display the text 'Edited!'

D. An error occurs because of wrong syntax

Solution

1. Step 1: Understand the trigger condition

   The function checks if the edited cell is 'A1' using e.range.getA1Notation().

2. Step 2: Analyze the action on condition true

   If true, it sets the value of cell 'B1' to 'Edited!' on the active sheet.

3. Final Answer:

   Cell B1 will display the text 'Edited!' -> Option C

4. Quick Check:

   Editing A1 triggers B1 = 'Edited!' [OK]

Hint: Check edited cell with e.range.getA1Notation() [OK]

Common Mistakes:

• Assuming the edited cell changes instead of B1
• Thinking the script clears A1
• Believing the code has syntax errors

4. This onOpen function is intended to show a custom menu, but it doesn't work:

function onOpen() {
  var ui = SpreadsheetApp.getUi;
  ui.createMenu('My Menu')
    .addItem('Say Hello', 'sayHello')
    .addToUi();
}

What is the error?

medium

A. Missing parentheses after getUi

B. Function onOpen must have parameter e

C. createMenu is not a valid method

D. addItem requires two parameters

Solution

1. Step 1: Identify method call syntax

   The code uses SpreadsheetApp.getUi without parentheses, so it references the function but does not call it.

2. Step 2: Correct method call

   Adding parentheses getUi() calls the method and returns the UI object needed to create the menu.

3. Final Answer:

   Missing parentheses after getUi -> Option A

4. Quick Check:

   Method calls need () to execute [OK]

Hint: Always add () to call methods like getUi() [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Thinking onOpen needs parameters
• Misunderstanding addItem parameters

5. You want to create an onEdit trigger that automatically timestamps column B when a user edits column A in the same row. Which script correctly does this?

hard

A. function onEdit(e) {
if (e.range.getColumn() === 2) {
var row = e.range.getRow();
e.source.getActiveSheet().getRange(row, 1).setValue(new Date());
}
}

B. function onEdit(e) {
if (e.range.getColumn() === 1) {
e.source.getActiveSheet().getRange('B' + e.range.getRow()).setValue('Timestamp');
}
}

C. function onEdit(e) {
if (e.range.getRow() === 1) {
e.source.getActiveSheet().getRange('B1').setValue(new Date());
}
}

D. function onEdit(e) {
if (e.range.getColumn() === 1) {
var row = e.range.getRow();
e.source.getActiveSheet().getRange(row, 2).setValue(new Date());
}
}

Solution

1. Step 1: Check column condition for edits in column A

   The script must detect edits in column 1 (A) using e.range.getColumn() === 1.

2. Step 2: Set timestamp in column B of the same row

   It gets the row number and sets the current date/time in column 2 (B) of that row using setValue(new Date()).

3. Final Answer:

   function onEdit(e) { if (e.range.getColumn() === 1) { var row = e.range.getRow(); e.source.getActiveSheet().getRange(row, 2).setValue(new Date()); } } -> Option D

4. Quick Check:

   Detect col A edit, timestamp col B same row [OK]

Hint: Use getColumn() and getRow() to target cells dynamically [OK]

Common Mistakes:

• Checking wrong column number for edits
• Using fixed cell references instead of dynamic rows
• Setting text instead of actual timestamp