Google Doc Change Notifier

code.gs

/**
 * 1. Go to script.google.com, and when logged in as the user that you want to do the "checking", click "➕ New Project" in the top right
 * 2. Copy/Paste all of this code into your new project, and give it a name (e.g. Google Doc Change Notifier)
 * 3. Change the `const docs = []` line to include all of the Docs you want to check. For example, `const docs = ["https://docs.google.com/document/blah", "https://docs.google.com/document/foo"];
 * 4. Click "▷ Run" in the toolbar and authorize the script to run.
 * 5. You're done!
 */

const docs = ["https://docs.google.com/document/d/1Gwt56BiconMLg_u-hdo0asdff27U7DlqLOzHVVgNnoM/edit"];

function check() {

  let properties = PropertiesService.getScriptProperties();

  for (let id of docs) {

    let document;
    try {
      document = DocumentApp.openById(id);
    } catch(e) {
      try {
        document = DocumentApp.openByUrl(id);
      }
      catch(e) {
        console.error('Cannot open the document "' + id + '" (' + e.message + '). Are you sure that\'s a doc? Do you have access to view it?');
        continue;
      }
    }

    let body = document.getBody().getText();
    console.log(body);

    let lastcheck = properties.getProperty(document.getId());
    
    let b64 = Utilities.computeDigest(Utilities.DigestAlgorithm.MD5, body, Utilities.Charset.UTF_8).reduce(function(str,chr){
      chr = (chr < 0 ? chr + 256 : chr).toString(16);
      return str + (chr.length==1?'0':'') + chr;
    },'');

    if (lastcheck !== b64) {
      MailApp.sendEmail(Session.getEffectiveUser().getEmail(), 'Document Has Changed', 'The Google Doc "' + document.getName() + '" has been edited. Check the Doc\'s Version History for more details. ' + document.getUrl());
      properties.setProperty(document.getId(), b64);
    }

  }

  verifyScheduled_();
}

function verifyScheduled_() {
  let triggers = ScriptApp.getProjectTriggers();
  if (!triggers.length || triggers.length >= 2 || triggers[0].getHandlerFunction() !== 'check') {
    console.warn('Deleting all existing triggers and rescheduling hourly trigger.');
    for (let trigger of triggers) {
      ScriptApp.deleteTrigger(trigger);
    }
    ScriptApp.newTrigger('check').timeBased().everyHours(1).create();
    console.info('Scheduled to run every hour!');
  }
}