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Google Apps Script

Build automation scripts for Google Sheets and Workspace apps. Scripts run server-side on Google's infrastructure with a generous free tier.

What You Produce

• Apps Script code pasted into Extensions > Apps Script
• Custom menus, dialogs, sidebars
• Automated triggers (on edit, time-driven, form submit)
• Email notifications, PDF exports, API integrations

Workflow

Step 1: Understand the Automation

Ask what the user wants automated. Common scenarios:

• Custom menu with actions (report generation, data processing)
• Auto-triggered behaviour (on edit, on form submit, scheduled)
• Sidebar app for data entry
• Email notifications from sheet data
• PDF export and distribution

Step 2: Generate the Script

Follow the structure template below. Every script needs a header comment, configuration constants at top, and onOpen() for menu setup.

Step 3: Provide Installation Instructions

All scripts install the same way:

1. Open the Google Sheet
2. Extensions > Apps Script
3. Delete any existing code in the editor
4. Paste the script
5. Click Save
6. Close the Apps Script tab
7. Reload the spreadsheet (onOpen runs on page load)

Step 4: First-Time Authorisation

Each user gets a Google OAuth consent screen on first run. For unverified scripts (most internal scripts), users must click:

Advanced > Go to Project Name] (unsafe) > Allow

This is a one-time step per user. Warn users about this in your output.

Script Structure Template

Every script should follow this pattern:

javascript
/**
 * [Project Name] - [Brief Description]
 *
 * [What it does, key features]
 *
 * INSTALL: Extensions > Apps Script > paste this > Save > Reload sheet
 */

// --- CONFIGURATION ---
const SOME_SETTING = 'value';

// --- MENU SETUP ---
function onOpen() {
  const ui = SpreadsheetApp.getUi();
  ui.createMenu('My Menu')
    .addItem('Do Something', 'myFunction')
    .addSeparator()
    .addSubMenu(ui.createMenu('More Options')
      .addItem('Option A', 'optionA'))
    .addToUi();
}

// --- FUNCTIONS ---
function myFunction() {
  // Implementation
}

Critical Rules

Public vs Private Functions

Functions ending with _ (underscore) are private and CANNOT be called from client-side HTML via google.script.run. This is a silent failure -- the call simply doesn't work with no error.

javascript
// WRONG - dialog can't call this, fails silently
function doWork_() { return 'done'; }

// RIGHT - dialog can call this
function doWork() { return 'done'; }

Also applies to: Menu item function references must be public function names as strings.

Batch Operations (Critical for Performance)

Read/write data in bulk, never cell-by-cell. The difference is 70x.

javascript
// SLOW (70 seconds on 100x100) - reads one cell at a time
for (let i = 1; i <= 100; i++) {
  const val = sheet.getRange(i, 1).getValue();
}

// FAST (1 second) - reads all at once
const allData = sheet.getRange(1, 1, 100, 1).getValues();
for (const row of allData) {
  const val = row[0];
}

Always use getRange().getValues() / setValues() for bulk reads/writes.

V8 Runtime

V8 is the only runtime (Rhino was removed January 2026). Supports modern JavaScript: const, let, arrow functions, template literals, destructuring, classes, async/generators.

NOT available (use Apps Script alternatives):

| Missing API | Apps Script Alternative | |-------------|------------------------| | setTimeout / setInterval | Utilities.sleep(ms) (blocking) | | fetch | UrlFetchApp.fetch() | | FormData | Build payload manually | | URL | String manipulation | | crypto | Utilities.computeDigest() / Utilities.getUuid() |

Flush Before Returning

Call SpreadsheetApp.flush() before returning from functions that modify the sheet, especially when called from HTML dialogs. Without it, changes may not be visible when the dialog shows "Done."

Simple vs Installable Triggers

| Feature | Simple (onEdit) | Installable | |---------|-------------------|-------------| | Auth required | No | Yes | | Send email | No | Yes | | Access other files | No | Yes | | URL fetch | No | Yes | | Open dialogs | No | Yes | | Runs as | Active user | Trigger creator |

Use simple triggers for lightweight reactions. Use installable triggers (via ScriptApp.newTrigger()) when you need email, external APIs, or cross-file access.

Custom Spreadsheet Functions

Functions used as =MY_FUNCTION() in cells have strict limitations:

javascript
/**
 * Calculates something custom.
 * @param {string} input The input value
 * @return {string} The result
 * @customfunction
 */
function MY_FUNCTION(input) {
  // Can use: basic JS, Utilities, CacheService
  // CANNOT use: MailApp, UrlFetchApp, SpreadsheetApp.getUi(), triggers
  return input.toUpperCase();
}

• Must include @customfunction JSDoc tag
• 30-second execution limit (vs 6 minutes for regular functions)
• Cannot access services requiring authorisation

Quotas and Limits

| Resource | Free Account | Google Workspace | |----------|-------------|-----------------| | Script runtime | 6 min / execution | 6 min / execution | | Time-driven trigger runtime | 30 min | 30 min | | Triggers total daily runtime | 90 min | 6 hours | | Triggers total | 20 per user per script | 20 per user per script | | Email recipients/day | 100 | 1,500 | | URL Fetch calls/day | 20,000 | 100,000 | | Properties storage | 500 KB | 500 KB | | Custom function runtime | 30 seconds | 30 seconds | | Simultaneous executions | 30 | 30 |

Modal Progress Dialog

Block user interaction during long operations with a spinner that auto-closes. Use for any operation taking more than a few seconds.

Pattern: menu function > showProgress() > dialog calls action function > auto-close

javascript
function showProgress(message, serverFn) {
  const html = HtmlService.createHtmlOutput(`
    <style>
      body { font-family: 'Google Sans', Arial, sans-serif; display: flex;
        flex-direction: column; align-items: center; justify-content: center;
        height: 100%; margin: 0; padding: 20px; box-sizing: border-box; }
      .spinner { width: 36px; height: 36px; border: 4px solid #e0e0e0;
        border-top: 4px solid #1a73e8; border-radius: 50%;
        animation: spin 0.8s linear infinite; margin-bottom: 16px; }
      @keyframes spin { to { transform: rotate(360deg); } }
      .message { font-size: 14px; color: #333; text-align: center; }
      .done { color: #1e8e3e; font-weight: 500; }
      .error { color: #d93025; font-weight: 500; }
    </style>
    <div class="spinner" id="spinner"></div>
    <div class="message" id="msg">${message}</div>
    <script>
      google.script.run
        .withSuccessHandler(function(r) {
          document.getElementById('spinner').style.display = 'none';
          var m = document.getElementById('msg');
          m.className = 'message done';
          m.innerText = 'Done! ' + (r || '');
          setTimeout(function() { google.script.host.close(); }, 1200);
        })
        .withFailureHandler(function(err) {
          document.getElementById('spinner').style.display = 'none';
          var m = document.getElementById('msg');
          m.className = 'message error';
          m.innerText = 'Error: ' + err.message;
          setTimeout(function() { google.script.host.close(); }, 3000);
        })
        .${serverFn}();
    </script>
  `).setWidth(320).setHeight(140);
  SpreadsheetApp.getUi().showModalDialog(html, 'Working...');
}

// Menu calls this wrapper
function menuDoWork() {
  showProgress('Processing data...', 'doTheWork');
}

// MUST be public (no underscore) for the dialog to call it
function doTheWork() {
  // ... do the work ...
  SpreadsheetApp.flush();
  return 'Processed 50 rows';  // shown in success message
}

Common Patterns

Toast Notifications

javascript
SpreadsheetApp.getActiveSpreadsheet().toast('Operation complete!', 'Title', 5);
// Arguments: message, title, duration in seconds (-1 = until dismissed)

Alert and Prompt Dialogs

javascript
const ui = SpreadsheetApp.getUi();

// Yes/No confirmation
const response = ui.alert('Delete this data?', 'This cannot be undone.',
  ui.ButtonSet.YES_NO);
if (response === ui.Button.YES) { /* proceed */ }

// Prompt for input
const result = ui.prompt('Enter your name:', ui.ButtonSet.OK_CANCEL);
if (result.getSelectedButton() === ui.Button.OK) {
  const name = result.getResponseText();
}

Sidebar Apps

HTML panel on the right. Use google.script.run to call server functions.

javascript
function showSidebar() {
  const html = HtmlService.createHtmlOutput(`
    <h3>Quick Entry</h3>
    <select id="worker"><option>Craig</option><option>Steve</option></select>
    <input id="suburb" placeholder="Suburb">
    <button onclick="submit()">Add Job</button>
    <script>
      function submit() {
        google.script.run.withSuccessHandler(function() { alert('Added!'); })
          .addJob(document.getElementById('worker').value,
                  document.getElementById('suburb').value);
      }
    </script>
  `).setTitle('Job Entry').setWidth(300);
  SpreadsheetApp.getUi().showSidebar(html);
}

function addJob(worker, suburb) { // MUST be public (no underscore)
  SpreadsheetApp.getActiveSpreadsheet().getActiveSheet().appendRow([new Date(), worker, suburb]);
}

Triggers

onEdit (simple trigger) -- limited permissions but no auth needed:

javascript
function onEdit(e) {
  const sheet = e.source.getActiveSheet();
  if (sheet.getName() !== 'Data') return;
  if (e.range.getColumn() !== 3) return;
  // Auto-timestamp when column C is edited
  sheet.getRange(e.range.getRow(), 4).setValue(new Date());
}

Installable triggers -- create via script, run setup function once manually:

javascript
function createTriggers() {
  // Time-driven: run every day at 8am
  ScriptApp.newTrigger('dailyReport')
    .timeBased().atHour(8).everyDays(1).create();

  // On edit with full permissions (can send email, fetch URLs)
  ScriptApp.newTrigger('onEditFull')
    .forSpreadsheet(SpreadsheetApp.getActive()).onEdit().create();

  // On form submit
  ScriptApp.newTrigger('onFormSubmit')
    .forSpreadsheet(SpreadsheetApp.getActive()).onFormSubmit().create();
}

Email from Sheets

javascript
function emailWeeklySchedule() {
  const sheet = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  const data = sheet.getRange('A2:E10').getDisplayValues();
  let body = '<h2>Weekly Schedule</h2><table border="1" cellpadding="8">';
  body += '<tr><th>Job</th><th>Suburb</th><th>Time</th><th>Price</th></tr>';
  for (const row of data) {
    if (row[0]) body += '<tr>' + row.map(c => '<td>' + c + '</td>').join('') + '</tr>';
  }
  body += '</table>';
  MailApp.sendEmail({ to: 'worker@example.com',
    subject: 'Schedule - Week ' + sheet.getName(), htmlBody: body });
}

PDF Export

Non-obvious URL construction -- export parameters are undocumented:

javascript
function exportSheetAsPdf() {
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  const url = ss.getUrl().replace(/\/edit.*$/, '')
    + '/export?exportFormat=pdf&format=pdf&size=A4&portrait=true'
    + '&fitw=true&sheetnames=false&printtitle=false&gridlines=false'
    + '&gid=' + ss.getActiveSheet().getSheetId();
  const blob = UrlFetchApp.fetch(url, {
    headers: { 'Authorization': 'Bearer ' + ScriptApp.getOAuthToken() }
  }).getBlob().setName('report.pdf');
  MailApp.sendEmail({ to: 'boss@example.com', subject: 'Weekly Report PDF',
    body: 'Attached.', attachments: [blob] });
}

External API Calls

javascript
// GET
function fetchData() {
  const r = UrlFetchApp.fetch('https://api.example.com/data', {
    headers: { 'Authorization': 'Bearer ' + getApiKey() } });
  return JSON.parse(r.getContentText());
}

// POST (muteHttpExceptions to handle errors yourself)
function postData(payload) {
  const r = UrlFetchApp.fetch('https://api.example.com/submit', {
    method: 'post', contentType: 'application/json',
    payload: JSON.stringify(payload), muteHttpExceptions: true });
  if (r.getResponseCode() !== 200) throw new Error('API error: ' + r.getContentText());
  return JSON.parse(r.getContentText());
}

Data Validation Dropdowns

javascript
// Dropdown from list
const rule = SpreadsheetApp.newDataValidation()
  .requireValueInList(['Option A', 'Option B', 'Option C'], true)
  .setAllowInvalid(false).setHelpText('Select an option').build();
sheet.getRange('C3:C50').setDataValidation(rule);

// Dropdown from range (e.g. a Lookups sheet)
const rule2 = SpreadsheetApp.newDataValidation()
  .requireValueInRange(ss.getSheetByName('Lookups').getRange('A1:A100')).build();
sheet.getRange('B3:B50').setDataValidation(rule2);

Properties Service (Persistent Storage)

Three scopes: PropertiesService.getScriptProperties() (shared), .getUserProperties() (per user), .getDocumentProperties() (per spreadsheet). All use .setProperty(key, value) / .getProperty(key). 500 KB limit.

Recipes

Auto-Archive Completed Rows

Move rows with "Complete" status to an Archive sheet. Processes bottom-up to avoid shifting row indices.

javascript
function archiveCompleted() {
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  const source = ss.getSheetByName('Active');
  const archive = ss.getSheetByName('Archive');
  const data = source.getDataRange().getValues();
  const statusCol = 4; // column E (0-indexed)

  for (let i = data.length - 1; i >= 1; i--) {
    if (data[i][statusCol] === 'Complete') {
      archive.appendRow(data[i]);
      source.deleteRow(i + 1); // +1 for 1-indexed rows
    }
  }
  SpreadsheetApp.flush();
}

Duplicate Detection and Highlighting

Pattern: read column with getValues(), track seen values in an object, highlight both the original and duplicate rows with setBackground('#f4cccc'). Process all data in one getValues() call, then set backgrounds individually (unavoidable for scattered highlights).

Batch Email Sender

Key pattern: check MailApp.getRemainingDailyQuota() before sending, mark status per row, wrap each send in try/catch.

javascript
function sendBatchEmails() {
  const sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Recipients');
  const data = sheet.getRange('A2:C' + sheet.getLastRow()).getValues(); // Email, Name, Status
  const remaining = MailApp.getRemainingDailyQuota();
  if (remaining < data.length) {
    SpreadsheetApp.getUi().alert('Only ' + remaining + ' emails left. Need ' + data.length);
    return;
  }
  let sent = 0;
  for (let i = 0; i < data.length; i++) {
    const [email, name, status] = data[i];
    if (!email || status === 'Sent') continue;
    try {
      MailApp.sendEmail({ to: email, subject: 'Your Weekly Update',
        htmlBody: '<p>Hi ' + name + ',</p><p>Here is your update...</p>' });
      sheet.getRange(i + 2, 3).setValue('Sent'); sent++;
    } catch (e) { sheet.getRange(i + 2, 3).setValue('Error: ' + e.message); }
  }
  SpreadsheetApp.flush();
}

Summary Dashboard Generator

Pattern: loop numbered weekly tabs (01-52), read summary cells from each, write aggregated rows into a Summary sheet. Use ss.getSheetByName(tabName) to iterate, ss.insertSheet('Summary') if it doesn't exist, summary.autoResizeColumns() at end, flush() before return.

Error Handling

Always wrap external calls in try/catch. Use muteHttpExceptions: true to handle HTTP errors yourself. Re-throw for dialog error handlers.

javascript
function fetchExternalData() {
  try {
    const response = UrlFetchApp.fetch('https://api.example.com/data', {
      headers: { 'Authorization': 'Bearer ' + getApiKey() },
      muteHttpExceptions: true
    });
    if (response.getResponseCode() !== 200)
      throw new Error('API returned ' + response.getResponseCode());
    return JSON.parse(response.getContentText());
  } catch (e) { Logger.log('Error: ' + e.message); throw e; }
}

Error Prevention

| Mistake | Fix | |---------|-----| | Dialog can't call function | Remove trailing _ from function name | | Script is slow on large data | Use getValues()/setValues() batch operations | | Changes not visible after dialog | Add SpreadsheetApp.flush() before return | | onEdit can't send email | Use installable trigger via ScriptApp.newTrigger() | | Custom function times out | 30s limit -- simplify or move to regular function | | setTimeout not found | Use Utilities.sleep(ms) (blocking) | | Script exceeds 6 min | Break into chunks, use time-driven trigger for batches | | Auth popup doesn't appear | User must click Advanced > Go to (unsafe) > Allow |

Debugging

• Logger.log() / console.log() -- View > Execution Log in Apps Script editor
• Run manually -- select function in editor dropdown > Run
• Executions tab -- shows all recent runs with errors and stack traces
• Trigger failures -- script.google.com > My Projects > Executions
• Always test on a copy of the sheet before deploying

Deployment Checklist

• ] All functions called from HTML dialogs are public (no trailing underscore)
• ] SpreadsheetApp.flush() called before returning from modifying functions
• ] Error handling (try/catch) around external API calls and MailApp
• ] Configuration constants at the top of the file
• ] Header comment with install instructions
• ] Tested on a copy of the sheet
• ] Considered multi-user behaviour (different permissions, different active sheet)
• ] Long operations use modal progress dialogs
• ] No hardcoded sheet names -- use configuration constants
• ] Checked email quota before batch sends

Reconstruct from Apps Script docs if needed

• Row/Column show/hide — sheet.hideRows(), showRows(), isRowHiddenByUser()
• Formatting — setBackground(), setFontWeight(), setBorder(), setNumberFormat(), conditional formatting
• Data protection — range.protect(), setUnprotectedRanges(), editor management
• Multiple sheets — getSheetByName(), looping numbered tabs, copyTo(), insertSheet()
• Auto-numbering rows — onEdit trigger to auto-number column A when column B is edited
• Google Chat webhooks — POST to chat.googleapis.com with JSON payload