JSONStream

What is JSONStream?

The JSONStream npm package is a Node.js module that provides a streaming JSON.parse and stringify. It allows you to parse large JSON files or streams chunk by chunk without loading the entire file into memory, and to stringify large objects into JSON streams.

What are JSONStream's main functionalities?

Parsing JSON Streams

This feature allows you to parse JSON data that is being streamed. You can use JSONStream.parse() to process a stream of JSON data and emit JavaScript objects.

{"_readableState":{"objectMode":true,"highWaterMark":16,"buffer":{"head":null,"tail":null,"length":0},"length":0,"pipes":null,"pipesCount":0,"flowing":null,"ended":false,"endEmitted":false,"reading":false,"sync":true,"needReadable":false,"emittedReadable":false,"readableListening":false,"resumeScheduled":false,"paused":true,"emitClose":true,"autoDestroy":true,"destroyed":false,"defaultEncoding":"utf8","awaitDrain":0,"readingMore":false,"decoder":null,"encoding":null},"readable":true,"_events":{},"_eventsCount":0,"_writableState":{"objectMode":true,"highWaterMark":16,"finalCalled":false,"needDrain":false,"ending":false,"ended":false,"finished":false,"destroyed":false,"decodeStrings":false,"defaultEncoding":"utf8","length":0,"writing":false,"corked":0,"sync":false,"bufferProcessing":false,"writecb":null,"writelen":0,"bufferedRequest":null,"lastBufferedRequest":null,"pendingcb":0,"prefinished":false,"errorEmitted":false,"emitClose":true,"autoDestroy":true,"bufferedRequestCount":0,"corkedRequestsFree":{"next":null,"entry":null}},"writable":true,"allowHalfOpen":true,"_transformState":{"needTransform":false,"transforming":false,"writecb":null,"writechunk":null,"writeencoding":null}}

Stringifying Objects to JSON Streams

This feature allows you to convert JavaScript objects into a JSON formatted stream. You can use JSONStream.stringify() to create a stream that outputs JSON data.

{"_readableState":{"objectMode":true,"highWaterMark":16,"buffer":{"head":null,"tail":null,"length":0},"length":0,"pipes":null,"pipesCount":0,"flowing":null,"ended":false,"endEmitted":false,"reading":false,"sync":true,"needReadable":false,"emittedReadable":false,"readableListening":false,"resumeScheduled":false,"paused":true,"emitClose":true,"autoDestroy":true,"destroyed":false,"defaultEncoding":"utf8","awaitDrain":0,"readingMore":false,"decoder":null,"encoding":null},"readable":true,"_events":{},"_eventsCount":0,"_writableState":{"objectMode":true,"highWaterMark":16,"finalCalled":false,"needDrain":false,"ending":false,"ended":false,"finished":false,"destroyed":false,"decodeStrings":false,"defaultEncoding":"utf8","length":0,"writing":false,"corked":0,"sync":false,"bufferProcessing":false,"writecb":null,"writelen":0,"bufferedRequest":null,"lastBufferedRequest":null,"pendingcb":0,"prefinished":false,"errorEmitted":false,"emitClose":true,"autoDestroy":true,"bufferedRequestCount":0,"corkedRequestsFree":{"next":null,"entry":null}},"writable":true,"allowHalfOpen":true,"_transformState":{"needTransform":false,"transforming":false,"writecb":null,"writechunk":null,"writeencoding":null}}

Other packages similar to JSONStream

stream-json

stream-json is a package similar to JSONStream that provides a streaming JSON parser and a set of stream components for different use cases. It is designed to be a more modular and flexible solution than JSONStream, allowing users to assemble the functionality they need.

big-json

big-json provides a way to parse and stringify large JSON files in a streaming fashion, similar to JSONStream. It uses JSONStream internally but adds a simpler API for reading and writing JSON files directly from and to the filesystem.

README

JSONStream

streaming JSON.parse and stringify

<img src=https://secure.travis-ci.org/dominictarr/JSONStream.png?branch=master>

example

var request = require('request')
  , JSONStream = require('JSONStream')
  , es = require('event-stream')

var parser = JSONStream.parse(['rows', true])
  , req = request({url: 'http://isaacs.couchone.com/registry/_all_docs'})
  , logger = es.mapSync(function (data) {
      console.error(data)
      return data
    })

in node 0.4.x

req.pipe(parser)
parser.pipe(logger)

in node v0.5.x

req.pipe(parser).pipe(logger)

JSONStream.parse(path)

usally, a json API will return a list of objects.

path should be an array of property names, RegExps, booleans, and/or functions. any object that matches the path will be emitted as 'data' (and piped down stream)

a 'root' event is emitted when all data has been received. The 'root' event passes the root object & the count of matched objects.

if path is empty or null, no 'data' events are emitted.

example

query a couchdb view:

curl -sS localhost:5984/tests/_all_docs&include_docs=true

you will get something like this:

{"total_rows":129,"offset":0,"rows":[
  { "id":"change1_0.6995461115147918"
  , "key":"change1_0.6995461115147918"
  , "value":{"rev":"1-e240bae28c7bb3667f02760f6398d508"}
  , "doc":{
      "_id":  "change1_0.6995461115147918"
    , "_rev": "1-e240bae28c7bb3667f02760f6398d508","hello":1}
  },
  { "id":"change2_0.6995461115147918"
  , "key":"change2_0.6995461115147918"
  , "value":{"rev":"1-13677d36b98c0c075145bb8975105153"}
  , "doc":{
      "_id":"change2_0.6995461115147918"
    , "_rev":"1-13677d36b98c0c075145bb8975105153"
    , "hello":2
    }
  },
]}

we are probably most interested in the rows.*.docs

create a Stream that parses the documents from the feed like this:

var stream = JSONStream.parse(['rows', true, 'doc']) //rows, ANYTHING, doc

stream.on('data', function(data) {
  console.log('received:', data);
});

stream.on('root', function(root, count) {
  if (!count) {
    console.log('no matches found:', root);
  }
});

awesome!

JSONStream.stringify(open, sep, close)

Create a writable stream.

you may pass in custom open, close, and seperator strings. But, by default, JSONStream.stringify() will create an array, (with default options open='[\n', sep='\n,\n', close='\n]\n')

If you call JSONStream.stringify(false) the elements will only be seperated by a newline.

If you only write one item this will be valid JSON.

If you write many items, you can use a RegExp to split it into valid chunks.

JSONStream.stringifyObject(open, sep, close)

Very much like JSONStream.stringify, but creates a writable stream for objects instead of arrays.

Accordingly, open='{\n', sep='\n,\n', close='\n}\n'.

When you .write() to the stream you must supply an array with [ key, data ] as the first argument.

numbers

There are occasional problems parsing and unparsing very precise numbers.

I have opened an issue here:

https://github.com/creationix/jsonparse/issues/2

+1

Acknowlegements

this module depends on https://github.com/creationix/jsonparse by Tim Caswell and also thanks to Florent Jaby for teaching me about parsing with: https://github.com/Floby/node-json-streams

license

MIT / APACHE2