The GridStore.write() method has a boolean 'close' parameter that is forwarded down to internal writeBuffer() function, where its value is never used:
https://github.com/mongodb/node-mongodb-native/blob/V1.3.23/lib/mongodb/gridfs/gridstore.js#L379

It seems to have been lost on this refactoring commit:
https://github.com/mongodb/node-mongodb-native/commit/365c6f89e24d3d4da9bd7b278b9c810838974779#diff-f22f442f1d0a1b1099198d646c619e9bL389

The parameter is documented in the source, but not in the example there:
http://mongodb.github.io/node-mongodb-native/markdown-docs/gridfs.html