Google Script to force update IMPORTXML cell function and populate into new row at regular time intervals.

RegularIntervalIMPORTXML.gs

// by u/NeutronStarsAreHeavy for Revoke Article 50 Petition Tracker.

// Function to check time, so that the save data function executes at specified times. Triggered every minute (set-up in GSuite Developer Hub)
function checkTime() {
  var now = new Date();
  var minute = now.getMinutes();
  if (minute == 00 || minute == 15 || minute == 30 || minute == 45) {
    
    // execute saveData
    saveData();
  }
  
  // terminate
  else {
    return;
  }
}

// Function to append IMPORTXML in cell(1,2) to force update. Inserts row before row(3) to populate with updated data. Calculates and populates other quanities of interest. 
function saveData() {
  var id = "1rgpDCb5Hsm2XGagN69TXpM-LW8A0gwD4xrozYgBjKDw";
  var ss = SpreadsheetApp.openById(id);
  var sheet = ss.getSheetByName("DATA");
  var dataRange = sheet.getDataRange();
  var formulas = dataRange.getFormulas();
  var content = "";
  var re = /.*[^a-z0-9]import(?:xml|data|feed|html|range)\(.*/gi;
  var re2 = /((\?|&)(update=[0-9]*))/gi;
  var re3 = /(",)/gi;
  var errors = 0;
  
  // insert new row (row3)
  sheet.insertRowsBefore(3,1);
  
  // add timestamp
  var timeZone = Session.getScriptTimeZone();
  var timestamp = Utilities.formatDate(new Date(),timeZone,"yyyy-MM-dd HH:mm");
  sheet.getRange(3,1).setValue(timestamp);
  
  // force IMPORTXML call
  do {
    var now = new Date();
    var time = now.getTime();
    content = formulas[0][1];
    if (content != "") {
      var match = content.search(re);
      if (match !== -1) {
        var updatedContent = content.toString().replace(re2,"$2update=" + time);
        if (updatedContent == content) {
          updatedContent = content.toString().replace(re3,"?update=" + time + "$1");
        }
        sheet.getRange(1,2).setFormula(updatedContent);
      }
    }
    var PetitionCount = sheet.getRange(1,2).getValue();
    if (isNaN(PetitionCount)) {
      Utilities.sleep(500);
      errors++;
    }
    else {
      break;
    }
  }
  while (errors!=0);
  
  // populate new row with updated IMPORTXML call
  sheet.getRange(3,2).setValue([[PetitionCount]]);
  
  // calculate and populate petition count change
  var PetitionCountChange = PetitionCount - sheet.getRange(4,2).getValue();
  sheet.getRange(3,3).setValue([[PetitionCountChange]]);
  
  // calculate and populate percentage of Leave votes
  var percentLeaveVoters = PetitionCount / 17410742;
  sheet.getRange(3,4).setValue([[percentLeaveVoters]]);
  
  // error messages
  if (PetitionCountChange == 0) {
    sheet.getRange(3,5).setValue("SOURCE NOT UPDATED");
  }
  if (sheet.getRange(3,2).isBlank()) {
    sheet.getRange(3,5).setValue("SOURCE UNAVAILABLE");
  }
   
}