[GAS] Fix Exception: Cannot call SpreadsheetApp.getUi() from this context

When automating Google Sheets with Google Apps Script (GAS), you may encounter the error "Exception: Cannot call SpreadsheetApp.getUi() from this context." This error is common when moving from manual execution to automated triggers.

Here is why it happens and how to fix it properly.

What the Error Means

Exception: Cannot call SpreadsheetApp.getUi() from this context.

This error means: "You cannot use UI elements (alerts, dialogs, menus) in the current execution method."

User Interfaces like alert, prompt, or toast require an active user session—meaning a human looking at the spreadsheet. If the script runs in the background, there is no one to show the alert to.

Common Causes

If you see this error in your logs (e.g., Execution started …), your script was likely triggered by one of the following:

• Time-driven triggers (e.g., runs every hour)
• onEdit / onChange triggers (simple triggers have limitations)
• Web Apps (doGet / doPost)
• API Executions
• Drive Triggers

In these background contexts, SpreadsheetApp.getUi() is strictly forbidden.

Typical Problematic Code

You likely have code similar to this running in a trigger:

// ❌ FAILS in triggers
SpreadsheetApp.getUi().alert('Finished!');

// ❌ FAILS in triggers
const ui = SpreadsheetApp.getUi();
ui.alert('Error occurred');

Solutions

1. Stop Using UI (Most Secure)

For automated triggers, the best solution is to remove all UI interactions. Background processes should run silently as much as possible.

Replace alerts with Logs:

// ✅ OK for triggers
Logger.log('Process finished');
console.log('Process finished');

Or write the status to a cell:

// ✅ OK for triggers
sheet.getRange('A1').setValue('Status: Finished');

2. Separate Core Logic from UI (Recommended)

This is the cleanest architecture. Split your code into a "Core" function (logic) and a "Manual" function (UI).

/**
 * Core function: Contains logic only. No UI calls.
 * Use this for TRIGGERS.
 */
function exportFileListToSheetCore() {
  // Logic to list files, write to sheet, etc.
  console.log('Core logic started...');
  // ...
  console.log('Core logic finished.');
}

/**
 * Wrapper function: Calls core logic and shows UI.
 * Use this for MANUAL execution (buttons/menus).
 */
function exportFileListToSheetManual() {
  exportFileListToSheetCore();
  SpreadsheetApp.getUi().alert('Process Completed!');
}

• Time-driven Trigger: Set it to run exportFileListToSheetCore.
• Button/Menu: Assign it to exportFileListToSheetManual.

This separation allows you to reuse the same logic for both automation and manual operation without errors.

3. Conditional Branching (Advanced)

If you must use a single function for both, wrap the UI call in a try-catch block to suppress the error in background contexts.

function safeAlert(message) {
  try {
    SpreadsheetApp.getUi().alert(message);
  } catch (e) {
    // If UI is unavailable (trigger execution), log instead
    console.log('Background execution (no UI): ' + message);
  }
}

【Conclusion】While this works, Solution 2 (Separation) is architecturally better and easier to maintain.

Summary

• 【Conclusion】getUi() cannot be used in triggers/automation.
• 【Point】UI is for "Human Operation" only.
• 【Fix】Separate your business logic from your UI logic.

Check your code around the line number reported in the error log (e.g., mainFunction.gs:2445) and remove or isolate the getUi() call using the methods above.