gistfile1.js

function(doc) {
  // stolen from 
  // https://github.com/sstephenson/prototype/blob/master/src/prototype/lang/object.js#L88
  function extend(destination, source) {
    for (var property in source)
      destination[property] = source[property];
    return destination;
  }

  var copy = extend({}, doc);

  delete copy._id;
  emit(null, copy);
}