Google Analytics Custom Task to save all hits to Google Sheets

function() {
  return function(model) {
       
    var globalSendTaskName = '_' + model.get('trackingId') + '_sendHitTask';
    
    // Hook the sendHitTask - grab an original reference to a function
    var originalSendTask = window[globalSendTaskName] = window[globalSendTaskName] || model.get('sendHitTask');
    model.set('sendHitTask', function(sendModel) { //overwrite sendHitTask with our code
      var hitPayload = sendModel.get('hitPayload');     
      
      //if(hitPayload.indexOf('&ti=') !== -1) { //Capture only Transaction hits
      if(hitPayload.indexOf('&t=timing') === -1) { //SkipTtimings hits

        //In the line below, replace YOUR-WEB_APP_URL with the Web App URL (provided to you when you published your Google Sheet web app)
        var baseUrl = YOUR-WEB_APP_URL;//'https://script.google.com/macros/s/AKfycbyLQZ8Wm_31V5EAnOT1BxGLfzJ1X2bsArqRxOc-xzg1NHqJBmVO/exec';
        var collectPayLoad = 'Date='+(new Date().toISOString());	//saving date (note, this is client-based time - be aware of timezones)
        collectPayLoad += '&Request=' + encodeURIComponent(sendModel.get('hitPayload'));	//save full request
        collectPayLoad += '&GAClientID=' + encodeURIComponent(sendModel.get('clientId'));	//save GA browser id/cookie
        collectPayLoad += '&User-Agent=' + encodeURIComponent(navigator.userAgent);			//save User-Agent
        //add your fields collection here

        //save dataLayer
        if(JSON && typeof JSON.stringify === 'function') {
          //JSON.stringify will fail if there are circular references in your dataLayer. 
          //to simplify the demo, I am not 
          var dlAsJSON = JSON.stringify(window.dataLayer);
          collectPayLoad += '&DataLayer=' + encodeURIComponent(dlAsJSON); //Data Layer as JSON. 
        }
        
        var collectUrl = baseUrl +'?'+ collectPayLoad;
        
        //Deliver data to our Google Sheet
        //In your real project you may consider to use navigator.sendBeacon delivery method
        var myImage = new Image();
        myImage.src = collectUrl;        
      }

      //Execute original
      originalSendTask(sendModel);
    });
    
  };
}