gistfile1.js

var _ = require('lodash');

Statuses
  .findAll()
  .sort({
    '$date': -1 //check if $ should be here and if -1 is the order you want
  })
  .then(function(statuses) {
  
    var timeOn = 0;
    
    var previousStatus = void 0;
    
    _.each(statuses, function(record) {
      var date = record.date.getTime(); //epoch millis
      
      // If first recorded event is falsy and there are no truthy events before it, do nothing as there's nothing to calculate
      if (record.status === 'away' && !previousStatus) return;
      
      // If status is away - let's calculate the difference between the previousStatus (that was `active`) to 
      // know how long user was using the app
      // and make previousStatus undefined again
      if (record.status === 'away') {
        timeOn += (date - previousState);
        previousState = void 0;
        
      // otherwise, set previousState to currentDate so we know when user started using the app    
      } else {
        previousState = date;
      }
      
    });
  
  });