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Overview

Google Apps Script is a cloud-based JavaScript platform that runs on Google’s servers. The wedding RSVP site uses it as a zero-cost backend — no server to provision, no hosting fees — that receives form submissions, writes rows to a Google Sheet, and dispatches email notifications via Gmail. Key reasons it was chosen:
  • Free — runs entirely within the Google Workspace quota
  • No server required — deployed as a Web App, accessible via a public HTTPS URL
  • Native Google Sheets integration — SpreadsheetApp reads and writes directly to the spreadsheet
  • Native Gmail integration — GmailApp sends confirmation and admin emails without any SMTP configuration
The SHEET_ID constant in the script must be replaced with the actual ID of your Google Sheet before deploying. The ID is the long string in the Sheet’s URL between /d/ and /edit.

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Constants

var SHEET_NAME = "RSVP_responses"; // Name of the sheet tab
var SHEET_ID   = "11Sp1j-FPY18T-WCTdqSCvMhP9ANqaCX12QXSsFlUhh8"; // REPLACE THIS
ConstantValuePurpose
SHEET_NAME"RSVP_responses"The tab name inside the Google Sheet
SHEET_ID(your sheet ID)Identifies which Google Sheet to open

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Functions

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doGet(e)

Handles HTTP GET requests sent to the Web App URL. Returns a JSON test response that confirms the script is live and reachable. 
function doGet(e) {
  return ContentService
    .createTextOutput(JSON.stringify({
      success: true,
      message: 'Google Apps Script is working',
      timestamp: new Date(new Date().getTime() + 8 * 60 * 60 * 1000)
                  .toISOString().replace('T', ' ').replace('Z', ' UTC+8'),
      method: 'GET'
    }))
    .setMimeType(ContentService.MimeType.JSON);
}
Response shape 
{
  "success": true,
  "message": "Google Apps Script is working",
  "timestamp": "2025-10-25 17:30:00.000 UTC+8",
  "method": "GET"
}
Open the Web App URL in a browser to verify the deployment is healthy.
Timestamps throughout the script are expressed in UTC+8 (Taiwan Standard Time). The offset is applied manually by adding 8 * 60 * 60 * 1000 milliseconds to the current UTC time before formatting.

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doPost(request)

The HTTP entry point for RSVP form submissions. Every POST from the frontend is routed here and immediately delegated to handleRequest. 
function doPost(request) {
  return handleRequest(request);
}
Keeping doPost thin makes the script easier to unit-test and extend: swap out handleRequest without touching the Web App entry point.

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handleRequest(request)

The core function. It acquires a concurrency lock, writes the submission to the sheet, triggers email notifications, and returns a JSON result. 
function handleRequest(request) {
  var lock = LockService.getPublicLock();
  lock.waitLock(30000); // wait up to 30 seconds

  try {
    var doc   = SpreadsheetApp.openById(SHEET_ID);
    var sheet = doc.getSheetByName(SHEET_NAME);

    var headRow = request.parameter.header_row || 1;
    var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0];
    var nextRow = sheet.getLastRow() + 1;
    var row     = [];

    for (i in headers) {
      if (headers[i] == "Timestamp") {
        var utc8Time = new Date(new Date().getTime() + 8 * 60 * 60 * 1000);
        row.push(utc8Time.toISOString().replace('T', ' ').replace('Z', ' UTC+8'));
      } else {
        row.push(request.parameter[headers[i]] || '');
      }
    }

    sheet.getRange(nextRow, 1, 1, row.length).setValues([row]);
    sendEmail(request.parameter);

    return ContentService
      .createTextOutput(JSON.stringify({ "result": "success", "message": "RSVP submitted successfully" }))
      .setMimeType(ContentService.MimeType.JSON);

  } catch(e) {
    return ContentService
      .createTextOutput(JSON.stringify({ "result": "error", "error": e.toString() }))
      .setMimeType(ContentService.MimeType.JSON);
  } finally {
    lock.releaseLock();
  }
}
Concurrency lock LockService.getPublicLock() creates a lock shared across all simultaneous executions of the script. waitLock(30000) blocks the current invocation for up to 30 seconds until the lock is free. This prevents two concurrent submissions from writing to the same row. The lock is always released in the finally block.

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setup()

A one-time initialisation function. Run it once from the Apps Script editor after pasting the script and setting SHEET_ID. 
function setup() {
  var doc = SpreadsheetApp.getActiveSpreadsheet();
  SCRIPT_PROP.setProperty("key", doc.getId());

  var initResult = initializeSheet();

  if (initResult.success) {
    console.log('Setup completed successfully');
  } else {
    console.error('Setup failed:', initResult.error);
  }

  return initResult;
}
1

Open the Apps Script editor

In your Google Sheet, go to Extensions → Apps Script.
2

Paste the script

Replace the default myFunction content with the full google-apps-script.js file content.
3

Set SHEET_ID

Replace the placeholder value of SHEET_ID with your sheet’s ID.
4

Run setup()

Select setup from the function dropdown and click Run. Grant the required permissions when prompted.

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initializeSheet()

Called by setup(). Creates the RSVP_responses sheet tab if it does not exist, writes the header row if missing, and applies column widths and data validation rules. Column widths set by initializeSheet()
ColumnHeaderWidth (px)
ATimestamp150
Bname200
Crelation150
Dattendance120
Eguests100
Fdietary150
Gvegetarian-meals150
Hchildren-seats150
Ichildren-seats-count150
Jinvitation150
Kaddress300
Lmessage300
Memail200
Data validation rules
ColumnAllowed valuesInvalid allowed?
D — attendanceyes, noNo
E — guests1, 2, 3, 4, 5Yes
C — relationfriends-groom, friends-bride, otherYes
F — dietary"", 1, 2Yes
G — vegetarian-meals"", 1, 2, 3, 4, 5Yes
H — children-seatsyes, noYes
I — children-seats-count"", 1, 2, 3, 4, 5Yes
J — invitationyes, noYes
Only attendance (column D) uses setAllowInvalid(false) — all other columns permit values outside the dropdown list.

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getRSVPStats()

Returns a summary of RSVP responses. Run it manually from the Apps Script editor to get a quick count. 
function getRSVPStats() {
  // returns:
  return {
    total: data.length,       // total number of responses
    attending: 0,             // count where attendance === 'yes'
    notAttending: 0,          // count where attendance === 'no'
    totalGuests: 0            // sum of guests for attending responses
  };
}
To use it: open the Apps Script editor, select getRSVPStats from the function dropdown, click Run, and inspect the execution log.

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testSetup()

A convenience test function. It verifies sheet access and sends a test email with dummy data. 
function testSetup() {
  // 1. Calls initializeSheet() and checks for success
  // 2. Opens the spreadsheet by SHEET_ID
  // 3. Accesses the RSVP_responses sheet
  // 4. Calls sendEmail() with a hardcoded test payload
}
Run testSetup() from the Apps Script editor after initial setup to confirm everything is wired correctly. Check the execution log for pass/fail messages and verify that a test email arrives at the admin address.

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POST request parameters

The frontend serialises the RSVP form and POSTs it to the Web App URL. All fields are sent as application/x-www-form-urlencoded string values.
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name
string
required
Full name of the guest submitting the RSVP.
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relation
string
Relationship to the couple. One of: friends-groom, friends-bride, other. Optional — not required by client-side validation.
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attendance
string
required
Whether the guest is attending. One of: yes, no.
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guests
string
required
Total number of guests in the party. Possible values: 0, 1, 2, 3, 4, 5, 6, 7, 99 (where 99 represents 8 or more guests — the “乾爹包桌” option).
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dietary
string
Dietary preference. One of: "" (regular), 1 (vegetarian), 2 (fasting).
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vegetarian-meals
string
Number of vegetarian meals needed. Required when dietary is 1. One of: 1, 2, 3.
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children-seats
string
Whether children’s high chairs are needed. One of: yes, no.
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children-seats-count
string
Number of children’s high chairs needed. Required when children-seats is yes. One of: 1, 2, 3.
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invitation
string
Whether a physical paper invitation is requested. One of: yes, no.
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address
string
Mailing address for the paper invitation. Required when invitation is yes.
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message
string
Optional message to the couple.
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email
string
Guest’s email address. If provided, a confirmation email is sent to this address.

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Response fields

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result
string
required
"success" on a successful write, "error" if an exception was caught.
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message
string
Human-readable status message. Present on success responses.
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error
string
Error message from the caught exception. Present only when result is "error".

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