Managing RSVPs with Google Apps Script

Code.gs

var SHEET_MAIN = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Form Responses 1');
var SHEET_RSVP = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('RSVPs');
var SHEET_EMAIL = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Invitees');

function onFormSubmit(e) {
  var range = e.range;
  var values = range.getValues();
  var row = values[0];

  var email = row[1];
  var validated = validateEmail(email);

  if (validated) {
    updateRSVPs(range, row);
  }
}

/**
 * Validate email against list of emails in worksheet.
 *
 * @return {Number} Index representing row position in the spreadsheet, or
 *  false if not found.
 */
function validateEmail(email) {
  return searchString(email, SHEET_EMAIL);
}

/**
 * Update RSVP worksheet with new submission.
 */
function updateRSVPs(range, row) {
  var columnCount = SHEET_MAIN.getLastColumn();
  var newResponseRange = SHEET_MAIN.getRange(range.getRow(), 1, 1, columnCount);

  var match_row = findInRow(row, SHEET_RSVP);

  if (match_row !== -1) {
    // Prepare to overwrite existing entry.
    var newResponseDestinationRange = SHEET_RSVP.getRange(match_row, 1, 1, columnCount);
  }
  else {
    // Prepare to create new entry.
    var newResponseDestinationRange = SHEET_RSVP.getRange(SHEET_RSVP.getLastRow()+1, 1, 1, columnCount);
  }

  // Write to spreadsheet.
  newResponseRange.copyTo(newResponseDestinationRange);
}

/**
 * Search the given sheet for a match against the submission.
 * Only compare two columns.
 *
 * @param {Array<String[]>} row An array of cell values for a row.
 * @param {Spreadsheet} sheet The spreadsheet that contains the RSVP data.
 * @return {Number} An index representing row position in the spreadsheet.
 */
function findInRow(row, sheet) {
  // Specify the column index of the email and id fields.
  var emailIndex = 1;
  var eventIdIndex = 4;

  // Combine the email and id columns into a string to compare against existing rows.
  var compare_row = row[emailIndex] + '#' + row[eventIdIndex];

  var range  = sheet.getDataRange();
  var rows  = range.getValues();

  for (var i = 0; i < rows.length; i++) {
    var each_row = rows[i][emailIndex] + '#' + rows[i][eventIdIndex];
    if (each_row.indexOf(compare_row) !== -1) {
      return i+1;
    }
  }
  return -1;
}


/**
 * Search for a string in a given worksheet.
 *
 * @param {String} search_string The string to search for.
 * @param {Spreadsheet} sheet The spreadsheet that contains the RSVP data.
 * @return {Number} Index representing row position in the spreadsheet, or
 *  false if not found.
 */
function searchString(search_string, sheet){
  var textFinder = sheet.createTextFinder(search_string);
  var search_row = textFinder.findNext();

  if (search_row) {
    return search_row.getRow();
  }

  return false;
}