discoveryjs
json-ext
A set of utilities designed to extend JSON's capabilities, especially for handling large JSON data (over 100MB) efficiently:
- parseChunked() – Parses JSON incrementally; similar to
JSON.parse(), but processing JSON data in chunks. - stringifyChunked() – Converts JavaScript objects to JSON incrementally; similar to
JSON.stringify(), but returns a generator that yields JSON strings in parts. - stringifyInfo() – Estimates the size of the
JSON.stringify()result and identifies circular references without generating the JSON. - parseFromWebStream() – A helper function to parse JSON chunks directly from a Web Stream.
- createStringifyWebStream() – A helper function to generate JSON data as a Web Stream.
Key Features
- Optimized to handle large JSON data with minimal resource usage (see benchmarks)
- Works seamlessly with browsers, Node.js, Deno, and Bun
- Supports both Node.js and Web streams
- Available in both ESM and CommonJS
- TypeScript typings included
- No external dependencies
- Compact size: 9.4Kb (minified), 3.8Kb (min+gzip)
Why json-ext?
- Handles large JSON files: Overcomes the limitations of V8 for strings larger than ~500MB, enabling the processing of huge JSON data.
- Prevents main thread blocking: Distributes parsing and stringifying over time, ensuring the main thread remains responsive during heavy JSON operations.
- Reduces memory usage: Traditional
JSON.parse()andJSON.stringify()require loading entire data into memory, leading to high memory consumption and increased garbage collection pressure.parseChunked()andstringifyChunked()process data incrementally, optimizing memory usage. - Size estimation:
stringifyInfo()allows estimating the size of resulting JSON before generating it, enabling better decision-making for JSON generation strategies.
Install
npm install @discoveryjs/json-extAPI
parseChunked()
Functions like JSON.parse(), iterating over chunks to reconstruct the result object, and returns a Promise.
Note:
reviverparameter is not supported yet.
function parseChunked(input: Iterable<Chunk> | AsyncIterable<Chunk>): Promise<any>;
function parseChunked(input: () => (Iterable<Chunk> | AsyncIterable<Chunk>)): Promise<any>;
type Chunk = string | Buffer | Uint8Array;Usage:
import { parseChunked } from '@discoveryjs/json-ext';
const data = await parseChunked(chunkEmitter);Parameter chunkEmitter can be an iterable or async iterable that iterates over chunks, or a function returning such a value. A chunk can be a string, Uint8Array, or Node.js Buffer.
Examples:
- Generator:
parseChunked(function*() { yield '{ "hello":'; yield Buffer.from(' "wor'); // Node.js only yield new TextEncoder().encode('ld" }'); // returns Uint8Array }); - Async generator:
parseChunked(async function*() { for await (const chunk of someAsyncSource) { yield chunk; } }); - Array:
parseChunked(['{ "hello":', ' "world"}']) - Function returning iterable:
parseChunked(() => ['{ "hello":', ' "world"}']) Node.js
Readablestream:import fs from 'node:fs'; parseChunked(fs.createReadStream('path/to/file.json'))- Web stream (e.g., using fetch()):
Note: Iterability for Web streams was added later in the Web platform, not all environments support it. Consider using
parseFromWebStream()for broader compatibility.const response = await fetch('https://example.com/data.json'); const data = await parseChunked(response.body); // body is ReadableStream
stringifyChunked()
Functions like JSON.stringify(), but returns a generator yielding strings instead of a single string.
Note: Returns
"null"whenJSON.stringify()returnsundefined(since a chunk cannot beundefined).
function stringifyChunked(value: any, replacer?: Replacer, space?: Space): Generator<string, void, unknown>;
function stringifyChunked(value: any, options: StringifyOptions): Generator<string, void, unknown>;
type Replacer =
| ((this: any, key: string, value: any) => any)
| (string | number)[]
| null;
type Space = string | number | null;
type StringifyOptions = {
replacer?: Replacer;
space?: Space;
highWaterMark?: number;
};Usage:
- Getting an array of chunks:
const chunks = [...stringifyChunked(data)]; - Iterating over chunks:
for (const chunk of stringifyChunked(data)) { console.log(chunk); } Specifying the minimum size of a chunk with
highWaterMarkoption:const data = [1, "hello world", 42]; console.log([...stringifyChunked(data)]); // default 16kB // ['[1,"hello world",42]'] console.log([...stringifyChunked(data, { highWaterMark: 16 })]); // ['[1,"hello world"', ',42]'] console.log([...stringifyChunked(data, { highWaterMark: 1 })]); // ['[1', ',"hello world"', ',42', ']']Streaming into a stream with a
Promise(modern Node.js):import { pipeline } from 'node:stream/promises'; import fs from 'node:fs'; await pipeline( stringifyChunked(data), fs.createWriteStream('path/to/file.json') );Wrapping into a
Promisestreaming into a stream (legacy Node.js):import { Readable } from 'node:stream'; new Promise((resolve, reject) => { Readable.from(stringifyChunked(data)) .on('error', reject) .pipe(stream) .on('error', reject) .on('finish', resolve); });Writing into a file synchronously:
Note: Slower than
JSON.stringify()but uses much less heap space and has no limitation on string length`js import fs from 'node:fs';const fd = fs.openSync('output.json', 'w');
for (const chunk of stringifyChunked(data)) {
fs.writeFileSync(fd, chunk);}
fs.closeSync(fd);
`Using with fetch (JSON streaming):
Note: This feature has limited support in browsers, see Streaming requests with the fetch API
Note:
ReadableStream.from()has limited support in browsers, usecreateStringifyWebStream()instead.fetch('http://example.com', { method: 'POST', duplex: 'half', body: ReadableStream.from(stringifyChunked(data)) });Wrapping into
ReadableStream:Note: Use
ReadableStream.from()orcreateStringifyWebStream()when no extra logic is needed`js new ReadableStream({start() { this.generator = stringifyChunked(data); }, pull(controller) { const { value, done } = this.generator.next();if (done) { controller.close(); } else { controller.enqueue(value); } }, cancel() { this.generator = null; }});
`
stringifyInfo()
export function stringifyInfo(value: any, replacer?: Replacer, space?: Space): StringifyInfoResult;
export function stringifyInfo(value: any, options?: StringifyInfoOptions): StringifyInfoResult;
type StringifyInfoOptions = {
replacer?: Replacer;
space?: Space;
continueOnCircular?: boolean;
}
type StringifyInfoResult = {
bytes: number; // size of JSON in bytes
spaceBytes: number; // size of white spaces in bytes (when space option used)
circular: object[]; // list of circular references
};Functions like JSON.stringify(), but returns an object with the expected overall size of the stringify operation and a list of circular references.
Example:
import { stringifyInfo } from '@discoveryjs/json-ext';
console.log(stringifyInfo({ test: true }, null, 4));
// {
// bytes: 20, // Buffer.byteLength('{\n "test": true\n}')
// spaceBytes: 7,
// circular: []
// }Options
continueOnCircular
Type: Boolean
Default: false
Determines whether to continue collecting info for a value when a circular reference is found. Setting this option to true allows finding all circular references.
parseFromWebStream()
A helper function to consume JSON from a Web Stream. You can use parseChunked(stream) instead, but @@asyncIterator on ReadableStream has limited support in browsers (see ReadableStream compatibility table).
import { parseFromWebStream } from '@discoveryjs/json-ext';
const data = await parseFromWebStream(readableStream);
// equivalent to (when ReadableStream[@@asyncIterator] is supported):
// await parseChunked(readableStream);createStringifyWebStream()
A helper function to convert stringifyChunked() into a ReadableStream (Web Stream). You can use ReadableStream.from() instead, but this method has limited support in browsers (see ReadableStream.from() compatibility table).
import { createStringifyWebStream } from '@discoveryjs/json-ext';
createStringifyWebStream({ test: true });
// equivalent to (when ReadableStream.from() is supported):
// ReadableStream.from(stringifyChunked({ test: true }))License
MIT