title: underscore _.each not adding property to object element
body: <p>This is kind of a newb question as there are still some small things about javascript that baffle me.</p>
  
  <p>I have the following code:</p>
  
  <pre><code>db.units.find({}, { _id: 1, type: 1, name: 1 }).sort({ type: 1, name: 1}).exec(function(err, units) {
  
    if(err) return next(err);
  
    _.each(units, function(u, i) {
      this[i]["available"] = !_.contains(_.pluck(_.pluck(req.workorder.units, 'unit'), 'name'), u.name);
  
      console.log(this[i].available);  
      console.log(this[i]);  
      console.log(_.extend(this[i],{available:this[i].available}));
    }, units); 
  
  
    return res.render('workorder/show', {
      workorder: req.workorder,
      invoices: db.invoices.find({ workorders: req.params.id }),
      units: units
    });
  });
  </code></pre>
  
  <p>and here is the result:</p>
  
  <p>true
  { _id: 513bd489b0e7e2634b60dc47,
    name: 'Visual Sump Inspection UST-22C NC',
    type: 'Service' }</p>
  
  <p>its is logging the available property but not in the object alone, why is this?</p>