json-stream-stringify

What is json-stream-stringify?

The json-stream-stringify npm package is designed to convert JavaScript objects into JSON strings in a memory-efficient manner by streaming the output. This is particularly useful for handling large objects that might otherwise consume too much memory if converted to JSON all at once.

What are json-stream-stringify's main functionalities?

Basic Usage

This feature demonstrates the basic usage of the json-stream-stringify package. It shows how to create a stream from a large JavaScript object and pipe it to a file, thereby converting the object to a JSON string in a memory-efficient way.

const JSONStreamStringify = require('json-stream-stringify');
const fs = require('fs');

const largeObject = { /* large object data */ };
const jsonStringifyStream = new JSONStreamStringify(largeObject);

jsonStringifyStream.pipe(fs.createWriteStream('output.json'));

Custom Replacer Function

This feature demonstrates how to use a custom replacer function with json-stream-stringify. The replacer function can be used to filter or modify the values being stringified. In this example, all string properties are excluded from the output.

const JSONStreamStringify = require('json-stream-stringify');
const fs = require('fs');

const largeObject = { /* large object data */ };
const replacer = (key, value) => {
  if (typeof value === 'string') {
    return undefined; // Exclude all string properties
  }
  return value;
};
const jsonStringifyStream = new JSONStreamStringify(largeObject, replacer);

jsonStringifyStream.pipe(fs.createWriteStream('output.json'));

Custom Space Argument

This feature demonstrates how to use the space argument to format the JSON output with indentation. In this example, the JSON output will be pretty-printed with an indentation of 2 spaces.

const JSONStreamStringify = require('json-stream-stringify');
const fs = require('fs');

const largeObject = { /* large object data */ };
const jsonStringifyStream = new JSONStreamStringify(largeObject, null, 2);

jsonStringifyStream.pipe(fs.createWriteStream('output.json'));

Other packages similar to json-stream-stringify

JSONStream

JSONStream is a package that provides streaming JSON parsing and stringifying. It is similar to json-stream-stringify in that it allows for memory-efficient handling of large JSON objects. However, JSONStream offers more flexibility with its ability to parse JSON streams in addition to stringifying them.

stream-json

stream-json is another package that provides tools for working with JSON in a streaming fashion. It includes parsers, stringifiers, and utilities for processing JSON data in a memory-efficient way. Compared to json-stream-stringify, stream-json offers a more modular approach with separate components for different tasks.

oboe

oboe is a library for working with JSON in a streaming manner. It allows for both parsing and stringifying JSON data. Oboe is particularly useful for handling large JSON responses from HTTP requests. Compared to json-stream-stringify, oboe provides more features for working with JSON data in real-time.

README

JSON Stream Stringify

JSON Stringify as a Readable Stream with rescursive resolving of any readable streams and Promises.

Now with typings!

Important and Breaking Changes in v2

• Completely rewritten from scratch
• 100% Code Coverage! 🎉
• Space argument finally implemented! 🎉
• ⚠️ Cycling is off by default
• ⚠️ JsonStreamStringify is now a constructor; use new operator
• Removed dependency on global JSON.stringify, Async/Await and Generators
• JsonStreamStringify is now compiled with babel to target ES5 (polyfills needed)
• Rejected promises and input stream errors are now handled and emitted as errors
• Added cyclic structure detection to prevent infinite recursion
• 🆕 Converted to Typescript

Main Features

• Promises are rescursively resolved and the result is piped through JsonStreamStringify
• Streams (Object mode) are recursively read and output as arrays
• Streams (Non-Object mode) are output as a single string
• Output is streamed optimally with as small chunks as possible
• Cycling of cyclical structures and dags using Douglas Crockfords cycle algorithm*
• Great memory management with reference release after processing and WeakMap/Set reference handling
• Optimal stream pressure handling
• Tested and runs on ES5**, ES2015**, ES2016 and later
• Bundled as UMD and Module

* Off by default since v2
** With polyfills

Install

npm install --save json-stream-stringify

# Optional if you need polyfills
# Make sure to include these if you target NodeJS <=v6 or browsers
npm install --save @babel/polyfill @babel/runtime

Usage

Using Node v8 or later with ESM / Webpack / Browserify / Rollup

No Polyfills, ESM

import JsonStreamStringify from 'json-stream-stringify';

Polyfilled, ESM

install @babel/runtime-corejs3 and corejs@3

import JsonStreamStringify from 'json-stream-stringify/module.polyfill';

Using Node >=8 / Other ES2015 UMD environments

const JsonStreamStringify = require('json-stream-stringify');

OR

const JsonStreamStringify = require('json-stream-stringify/umd');

Using Node <=6 / Other ES5 UMD environments

var JsonStreamStringify = require('json-stream-stringify/umd.polyfill');

Note: This library is primarily written for LTS versions of NodeJS. Other environments are not tested.
Note on non-NodeJS usage: This module depends on node streams library. Any Streams3 compatible implementation should work - as long as it exports a Readable class, with instances that looks like readable streams.
Note on Polyfills: I have taken measures to minify global pollution of polyfills but this library does not load polyfills by default because the polyfills modify native object prototypes and it goes against the W3C recommendations.

API

new JsonStreamStringify(value[, replacer[, spaces[, cycle]]])

Streaming conversion of value to JSON string.

Parameters

• value Any
  Data to convert to JSON.

• replacer Optional Function(key, value) or Array
  As a function the returned value replaces the value associated with the key. Details
  As an array all other keys are filtered. Details

• spaces Optional String or Number
  A String or Number object that's used to insert white space into the output JSON string for readability purposes. If this is a Number, it indicates the number of space characters to use as white space. If this is a String, the string is used as white space. If this parameter is not recognized as a finite number or valid string, no white space is used.

• cycle Optional Boolean
true enables cycling of cyclical structures and dags.
  To restore cyclical structures; use Crockfords Retrocycle method on the parsed object (not included in this module).

Returns

• JsonStreamStringify object that exposes a Streams3 interface.

jsonStreamStringify#path

Get current path begin serialized.

Returns

• Array[String, Number]
  Array of path Strings (keys of objects) and Numbers (index into arrays).
  Can be transformed into an mpath with .join('.').
  Useful in conjunction with .on('error', ...), for figuring out what path may have caused the error.

Example Usage

const JsonStreamStringify = require('json-stream-stringify');

const jsonStream = new JsonStreamStringify({
    // Promises and Streams may resolve more promises and/or streams which will be consumed and processed into json output
    aPromise: Promise.resolve(Promise.resolve("text")),
    aStream: ReadableObjectStream({a:1}, 'str'),
    arr: [1, 2, Promise.resolve(3), Promise.resolve([4, 5]), ReadableStream('a', 'b', 'c')],
    date: new Date(2016, 0, 2)
});
jsonStream.once('error', () => console.log('Error at path', jsonStream.stack.join('.')));
jsonStream.pipe(process.stdout);

Output (each line represents a write from jsonStreamStringify)

{
"aPromise":
"text"
"aStream":
[
{
"a":
1
}
,
"str"
]
"arr":
[
1
,
2
,
3
,
[
4
,
5
]
,
"
a
b
c
"
],
"date":
"2016-01-01T23:00:00.000Z"
}

Practical Example with Express + Mongoose

app.get('/api/users', (req, res, next) => {
  res.type('json'); // Required for proper handling by test frameworks and some clients
  new JsonStreamStringify(Users.find().stream()).pipe(res);
});

License

MIT

Copyright (c) 2016 Faleij [e-mail]