Companion snippet for https://www.impression.co.uk/blog/8753/monitoring-website-uptime-google-sheets-email-alerts/

Google Sheets Script uptime checker

/**
 * Website uptime checker for clients at Impression
 * Inspired by Labnol's solution (https://lifehacker.com/5896830/use-google-docs-to-monitor-your-websites-uptime)
 * By aaron@impression.co.uk for https://www.impression.co.uk
 */ 

function init() {  
  if (ScriptApp.getProjectTriggers().length == 0) {
    ScriptApp.newTrigger("websiteMonitor").timeBased().everyMinutes(1).create();
  }  
}

function websiteMonitor() { 
  var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Config");
  var lastRow = sheet.getLastRow();
  Logger.log('last'+lastRow);
  var configuration = sheet.getRange(2, 1, lastRow-1, 3);
  var config_vars = configuration.getValues();
  var response, code, msg, status;  
  var time  = new Date(); 
  eval(UrlFetchApp.fetch('https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.19.2/moment.min.js').getContentText());
  
  for (var i in config_vars) {
    var emails = config_vars[i][1].replace(/\s/g, "").split(","); 
    var url = config_vars[i][0];
    
    try {    
      response = UrlFetchApp.fetch(url);
      code = response.getResponseCode();
    } catch(error) {
      // If URLFetchApp fails, the site is probably down
      code = 404;
    }
    
    if (parseInt(code) > 200) {
      msg = url+" is down";
      status = "DOWN";
      if (PropertiesService.getScriptProperties().getProperty(url) ) {
        // Still down
        // logSiteChanges(url, 'DOWN_STILL');
      } else {
        // Just gone down
        PropertiesService.getScriptProperties().setProperty(url, time);
        logSiteChanges(url, 'DOWN');
        
        for (var e in emails) {
          MailApp.sendEmail(emails[e], msg, msg);
        }
      }
    } else {
      msg = url+" is up";
      status = "UP";
      if (PropertiesService.getScriptProperties().getProperty(url) ) {
        var time_down = moment(PropertiesService.getScriptProperties().getProperty(url)); 
        var duration = moment.duration(moment().diff(time_down)).asMinutes();
        
        logSiteChanges(url, 'UP after '+duration+' minutes'); 
        msg = url+" is after "+duration+" minutes";
        
        logSiteChanges(url, 'UP after '+duration+' minutes'); 
        
        // No longer down 
        PropertiesService.getScriptProperties().deleteProperty(url);
        
        for (var e in emails) {
          MailApp.sendEmail(emails[e], msg, msg);
        }
      } 
    }
    sheet.getRange(parseInt(i)+2, 3).setValue(status+": "+url);
    
  }
}

function logSiteChanges(url, status) {
  var time  = new Date();
  var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Log");
  sheet.appendRow([time, url, status]);
}