Gmail autoarchive by label

Code.gs

// Will be checked against lowercased label names
var autoarchiveLabels = {
  newsletters: 2
};

// Get cutoff date for a specific label
function labelDelayDate(labelName) {
  if (!autoarchiveLabels[labelName.toLowerCase()]) {
    return false;
  }
  var delayDays = autoarchiveLabels[labelName.toLowerCase()];
  var maxDate = new Date();
  maxDate.setDate(maxDate.getDate() - delayDays);
  return maxDate;
}

// Archive thread after cutoff dat
function shouldArchive(thread, label) {
  var maxDate = labelDelayDate(label.getName());
  if (!maxDate) {
    return false;
  }
  
  // Being in the inbox already is implicit but helps with logging
  // on the threads that are affected
  var shouldArchive = thread.getLastMessageDate() < maxDate && thread.isInInbox();

  if (shouldArchive) {
    Logger.log('Will archive: ' + thread.getFirstMessageSubject());
  }

  return shouldArchive;
}

// Check threads against cutoff date and archive them
function archiveLabel(label) {    
  Logger.log('Archiving ' + label.getName());
  var threads = label.getThreads(0, 100).filter(
    function (thread) { return shouldArchive(thread, label) }
  );
  Logger.log('Found ' + threads.length + ' archivable threads');
  if (threads.length) {
    GmailApp.moveThreadsToArchive(threads);
  }
}

// Loop through archivable labels
function gmailAutoarchive() {  
  var labels = GmailApp.getUserLabels();
  for (var i = 0; i < labels.length; i++) {
    var label = labels[i];
    if (Object.keys(autoarchiveLabels).indexOf(label.getName().toLowerCase()) !== -1) {
      archiveLabel(label);
    }
  }
}