gmailAutoarchive.gs

var DAYS = 24;

function gmailAutoarchive() {
  processesLabel(12, "merged", archive);
  processesLabel(7*DAYS, "OOO", archive);
  processesLabel(20, "daily", archive);
  processesLabel(7*DAYS, "Etc.", markRead);
}

var MILLIS_PER_HOUR = 1000 * 60 * 60;

function processesLabel(delayHours, labelName, action) { 
  var maxDate = new Date((new Date()).getTime() - (delayHours*MILLIS_PER_HOUR));

  // Get all the labelled threads
  var label = GmailApp.getUserLabelByName(labelName);
  var threads = label.getThreads(0, 400);
  
  // Take action on threads if they're older than the limit set in delayHours
  for (var i = 0; i < threads.length; i++) {
    if (threads[i].getLastMessageDate()<maxDate) {
      action(threads[i]);
    }
  }
}

function archive(thread) {
  thread.moveToArchive();
}

function markRead(thread) {
  thread.markRead();
}