StreamObject

StreamObject assumes that a token stream represents an object and streams out its top-level properties as assembled JavaScript objects.

{"a": 1, "b": "a", "c": [], "d": {}, "e": true}
// StreamObject will produce an object stream:
{key: 'a', value: 1}
{key: 'b', value: 'a'}
{key: 'c', value: []}
{key: 'd', value: {}}
{key: 'e', value: true}

As every streamer, it assumes that individual objects can fit in memory, but the whole file, or any other source, should be streamed.

Warning: it cannot be used with a stream of objects produced by a JSON Streaming source, or Pick if it picks more than one object.

Introduction

const {streamObject} = require('stream-json/streamers/stream-object.js');
const fs = require('fs');

const pipeline = fs.createReadStream('sample.json').pipe(streamObject.withParserAsStream());

pipeline.on('data', data => console.log(data));

API

Being based on StreamBase, StreamObject has no special API.

Static methods and properties

streamObject(options)

streamObject() is the factory function. It takes options described above and returns a function for use in chain():

const {chain} = require('stream-chain');
const {parser} = require('stream-json');
const {streamObject} = require('stream-json/streamers/stream-object.js');

const fs = require('fs');

const pipeline = chain([fs.createReadStream('sample.json'), parser(), streamObject()]);

let objectCounter = 0;
pipeline.on('data', () => ++objectCounter);
pipeline.on('end', () => console.log(`Found ${objectCounter} objects.`));

streamObject.asStream(options)

Returns a Duplex stream (object-mode both sides) wrapping streamObject() for .pipe() usage.

withParser()

withParser() takes one argument:

• options — combined Parser and streamer options. Passed to both the parser and streamObject().

Returns a Duplex stream (text-mode writable, object-mode readable) wrapping a parser() + streamObject() pipeline via stream-chain.

Built with the withParser() utility.

const {streamObject} = require('stream-json/streamers/stream-object.js');
const fs = require('fs');

const pipeline = fs.createReadStream('sample.json').pipe(streamObject.withParserAsStream());

let objectCounter = 0;
pipeline.on('data', () => ++objectCounter);
pipeline.on('end', () => console.log(`Found ${objectCounter} objects.`));

Web Streams

streamObject ships in two substrate-specific entries with the same factory shape:

• Node — stream-json/streamers/stream-object.js. Has asStream, asWebStream, withParser, withParserAsStream, withParserAsWebStream.
• Web — stream-json/web/streamers/stream-object.js. Has asWebStream, withParser, withParserAsWebStream. Pulls in no Node-stream imports.

Both factories return the same flushable, so chain on either substrate auto-wraps it. Use chain from stream-chain on Node and from stream-chain/web on Web.

// Web
import {chain} from 'stream-chain/web';
import {parser} from 'stream-json/web/parser.js';
import {streamObject} from 'stream-json/web/streamers/stream-object.js';

const pipeline = chain([source, parser(), streamObject()]);
for await (const {key, value} of pipeline.readable) console.log(key, value);

Or the parser-included shortcut:

const {readable, writable} = streamObject.withParserAsWebStream();
sourceReadable.pipeTo(writable);
for await (const item of readable) console.log(item);