mongomapreduce.js

var MongoClient = require('mongodb').MongoClient;    

var mapFn = function() {
  emit(1, { length: this.length });
}

var reduceFn = function(key, values) {
  var sum = 0;
  values.forEach(function(doc) {
    sum += doc.length;
  });
  return { totalLength: sum };
};

MongoClient.connect('mongodb://10.1.4.175:27017/test', function(err, db) {
  if(err) throw err;

  var MR = {
    mapreduce: "beards", 
    out:  {inline: 1},
    map: mapFn.toString(),
    reduce: reduceFn.toString()
  }

  db.executeDbCommand(MR, function(err, dbres) {
    console.log(dbres);
    var results = dbres.documents[0].results
    console.log("executing map reduce, results:")
    console.log(JSON.stringify(results))
    process.exit(1)
  });
});