Actual documentation from MongoDB. This was a "simple example". http://mongodb.github.io/node-mongodb-native/api-generated/gridstore.html

wat.js

var Db = require('mongodb').Db,
    MongoClient = require('mongodb').MongoClient,
    Server = require('mongodb').Server,
    ReplSetServers = require('mongodb').ReplSetServers,
    ObjectID = require('mongodb').ObjectID,
    Binary = require('mongodb').Binary,
    GridStore = require('mongodb').GridStore,
    Grid = require('mongodb').Grid,
    Code = require('mongodb').Code,
    BSON = require('mongodb').pure().BSON,
    assert = require('assert');

var db = new Db('test', new Server('locahost', 27017));
// Establish connection to db
db.open(function(err, db) {
  // Create a file and open it
  var gridStore = new GridStore(db, new ObjectID(), "test_gs_getc_file", "w");
  gridStore.open(function(err, gridStore) {
    // Write some content to the file
    gridStore.write(new Buffer("hello, world!", "utf8"), function(err, gridStore) {
      // Flush the file to GridFS
      gridStore.close(function(err, fileData) {
        assert.equal(null, err);

        // Create another file with same name and and save content to it
        gridStore = new GridStore(db, new ObjectID(), "test_gs_getc_file", "w");
        gridStore.open(function(err, gridStore) {
          // Write some content to the file
          gridStore.write(new Buffer("hello, world!", "utf8"), function(err, gridStore) {
            // Flush the file to GridFS
            gridStore.close(function(err, fileData) {
              assert.equal(null, err);

              // Open the file in read mode using the filename
              var gridStore2 = new GridStore(db, "test_gs_getc_file", "r");
              gridStore2.open(function(err, gridStore) {

                // Read first character and verify
                gridStore.getc(function(err, chr) {
                  assert.equal('h', chr);

                  // Open the file using an object id
                  gridStore2 = new GridStore(db, fileData._id, "r");
                  gridStore2.open(function(err, gridStore) {

                    // Read first character and verify
                    gridStore.getc(function(err, chr) {
                      assert.equal('h', chr);

                      db.close();
                    })
                  });
                });
              });
            });
          });
        });
      });
    });
  });
});