promise-question.js

db.user_invoices.findAysnc({
  status: 'pending'
, billing_period_begin: period.startDate
, billing_period_end:   period.endDate
})
.catch( function( error ){ throw error; });
.map( function( invoice ){
  return invoices.create( invoice )
    .sendEmailAsync()
    .error( function( error ){
      errors.push( error );
    });
}, { concurrency: CONCURRENCY })
.then( function(){

});