mongodb-jsMongoDB Extended JSON Library 
The MongoDB Extended JSON Library allows you to convert MongoDB documents to Extended JSON, and vice versa. See the Extended JSON specification here.
Usage with MongoDB Driver
This library can be used along with the MongoDB driver for Node.js to convert MongoDB documents to extended JSON form.
Serialize a document
Serialize a document using EJSON.stringify(value, reducer, indents, options). The reducer and indents arguments are analogous to JSON.stringify's replacer and spaces arguments, respectively (see documentation.)
options currently supports a single option, relaxed; with options = {relaxed: true}, the returned object will be in the more readable "relaxed" extended JSON format.
let EJSON = require('mongodb-extjson'),
Int32 = require('mongodb').Int32;
var doc = { int32: new Int32(10) };
// prints '{"int32":{"$numberInt":"10"}}'
console.log(EJSON.stringify(doc));
// prints '{"int32":10}'
console.log(EJSON.stringify(doc, {relaxed: true}));
Usage with MongoDB BSON Library
Our js-bson library is included as a dependency and used by default for Javascript representations of BSON types. See the next section for instructions on using it with a different BSON library.
Serialize a document
This works identically to the previous serialize example, but does not require including the MongoDB driver. The BSON types are all available under EJSON.BSON.
let EJSON = require('mongodb-extjson'),
Int32 = EJSON.BSON.Int32;
var doc = { int32: new Int32(10) };
// prints '{"int32":{"$numberInt":"10"}}'
console.log(EJSON.stringify(doc));
Deserialize a document
The library also allows converting extended JSON strings to Javascript objects, using BSON type classes defined in js-bson. You can do this using EJSON.parse(string, options).
This method supports the option strict. By default, strict is true; if strict is set to false, the parser will attempt to return native JS types where possible, rather than BSON types (i.e. return a Number instead of a BSON.Int32 object, etc.)
let EJSON = require('mongodb-extjson');
var text = '{"int32":{"$numberInt":"10"}}';
// prints { int32: { [String: '10'] _bsontype: 'Int32', value: '10' } }
console.log(EJSON.parse(text));
// prints { int32: 10 }
console.log(EJSON.parse(text, {strict: false}));
Usage With Other BSON Parsers
Although we include the pure Javascript BSON parser by default, you can also use a different BSON parser with this library, such as bson-ext. For example:
let EJSON = require('mongodb-extjson'),
BSON = require('bson-ext'),
Int32 = BSON.Int32;
// set BSON module to be bson-ext
EJSON.setBSONModule(BSON);
var doc = { int32: new Int32(10) };
// prints '{"int32":{"$numberInt":"10"}}'
console.log(EJSON.stringify(doc));
var text = '{"int32":{"$numberInt":"10"}}';
// prints { int32: { [String: '10'] _bsontype: 'Int32', value: '10' } }
console.log(EJSON.parse(text));