@json2csv/whatwg

Fast and highly configurable JSON to CSV converter. It fully support conversion following the RFC4180 specification as well as other similar text delimited formats as TSV.

@json2csv/whatwg exposes two modules to integrate json2csv with the WHATWG Stream API for stream processing of JSON data.

This package includes two modules:

• WHATWG Transform Stream: WHATWG Transform Stream that ingests JSON and outputs csv. Ideal to process streams (http responses, file contents, ...) in WHATWG-compliant systems like the browser, Deno or even Node.js.
• WHATWG Async Parser: Wraps the Node Transform to offer a friendly promise-based API.

Features

• Fast and lightweight
• Support for standard JSON as well as NDJSON
• Scalable to infinitely large datasets (using stream processing)
• Advanced data selection (automatic field discovery, underscore-like selectors, custom data getters, default values for missing fields, ...)
• Support for custom input data transformation
• Support for custom csv cell formatting.
• Highly customizable (supporting custom quotation marks, delimiters, eol values, etc.)
• Automatic escaping (preserving new lines, quotes, etc.)
• Optional headers
• Unicode encoding support
• Pretty printing in table format to stdout

Other json2csv packages

There are multiple flavours of json2csv:

• Plainjs: Includes the Parser API and a new StreamParser API which doesn't the conversion in a streaming fashion in pure js.
• Node: Includes the Node Transform and Node Async Parser APIs for Node users.
• WHATWG: Includes the WHATWG Transform Stream and WHATWG Async Parser APIs for users of WHATWG streams (browser, Node or Deno).
• CLI: Includes the CLI interface.

And a couple of libraries that enable additional configurations:

• Transforms: Includes the built-in transforms for json2csv (unwind and flatten) allowing the using to transform data before is parsed.
• Formatters: Includes the built-in formatters for json2csv (one for each data type, an excel-specific one, etc.). Formatters convert JSON data types into CSV-compatible strings.

Requirements

• None

Installation

NPM

You can install json2csv as a dependency using NPM.

$ npm install --save @json2csv/whatwg

Yarn

You can install json2csv as a dependency using Yarn.

$ yarn add --save @json2csv/whatwg

CDN

json2csv WHATWG modules are packaged as ES6 modules. If your browser supports modules, you can load json2csv WHATWG modules directly on the browser from the CDN.

You can import the latest version:

<script type="module">
  import AsyncParser from 'https://cdn.jsdelivr.net/npm/@json2csv/whatwg/src/AsyncParser.js';
  import TransformStream from 'https://cdn.jsdelivr.net/npm/@json2csv/whatwg/src/TransformStream.js';
</script>

You can also select a specific version:

<script type="module">
  import AsyncParser from 'https://cdn.jsdelivr.net/npm/@json2csv/[email protected]/src/AsyncParser.js';
  import TransformStream from 'https://cdn.jsdelivr.net/npm/@json2csv/[email protected]/src/TransformStream.js';
</script>

WHATWG Transform Stream

For browser users, the Streaming API is wrapped in a WHATWG Transform Stream. This approach ensures a consistent memory footprint and avoids blocking JavaScript's event loop.

The async API takes a second options arguments that is directly passed to the underlying streams accepts the same options as the Stream Parser. It also support a third and fourth options equivalent to the writableStrategy and readableStrategy of a WHATWG Transform Stream respectively.

This Transform uses the StreamParser under the hood and support similar events.

Usage

import { TransformStream } from '@json2csv/whatwg';

const opts = {};
const asyncOpts = {};
const writableStrategy = {};
const readableStrategy = {};
const parser = new TransformStream(opts, asyncOpts, writableStrategy, readableStrategy);

const response = await fetch('./my-file.json');

await response.body.pipeThrough(parser).pipeTo(writableStream);

// You can also listen for events on the conversion and see how the header or the lines are coming out.
parser
  .addEventListener('header', (header) => console.log(header))
  .addEventListener('line', (line) => console.log(line));

Parameters

Options

• ndjson <Boolean> indicates that the data is in NDJSON format. Only effective when using the streaming API and not in object mode.
• fields <DataSelector[]> Defaults to toplevel JSON attributes.
• transforms <Transform[]> Array of transforms to apply to the data. A transform is a function that receives a data recod and returns a transformed record. Transforms are executed in order.
• formatters <Formatters> Object where the each key is a Javascript data type and its associated value is a formatters for the given type.
• defaultValue <Any> value to use when missing data. Defaults to <empty> if not specified. (Overridden by fields[].default)
• delimiter <String> delimiter of columns. Defaults to , if not specified.
• eol <String> overrides the default OS line ending (i.e. \n on Unix and \r\n on Windows).
• header <Boolean> determines whether or not CSV file will contain a title column. Defaults to true if not specified.
• includeEmptyRows <Boolean> includes empty rows. Defaults to false.
• withBOM <Boolean> with BOM character. Defaults to false.

Async Options

Options used by the underlying parsing library to process the binary or text stream. Not relevant when running in objectMode. Buffering is only relevant if you expect very large strings/numbers in your JSON. See @streamparser/json for more details about buffering.

• stringBufferSize <number> Size of the buffer used to parse strings. Defaults to 0 which means to don't buffer. Min valid value is 4.
• numberBufferSize <number> Size of the buffer used to parse numbers. Defaults to 0 to don't buffer.

Writable Strategy

An object that optionally defines a queuing strategy for the stream. See Writable Strategy in MDN for more details.

• highWaterMark <number> A non-negative integer. This defines the total number of chunks that can be contained in the internal queue before backpressure is applied.
• size (chunk) => {} A method containing a parameter chunk. This indicates the size to use for each chunk, in bytes.

Readable Strategy

An object that optionally defines a queuing strategy for the stream. See Readable Strategy in MDN for more details.

• highWaterMark <number> A non-negative integer. This defines the total number of chunks that can be contained in the internal queue before backpressure is applied.
• size (chunk) => {} A method containing a parameter chunk. This indicates the size to use for each chunk, in bytes.

Complete Documentation

See https://juanjodiaz.github.io/json2csv/#/parsers/whatwg-transform-stream.

WHATWG Async Parser

To facilitate usage, WHATWGAsyncParser wraps WHATWGTransformStream exposing a single parse method similar to the sync API. This method accepts JSON arrays/objects, TypedArrays, strings and readable streams as input and returns a stream that produces the CSV.

WHATWGAsyncParser also exposes a convenience promise method which turns the stream into a promise that resolves to the whole CSV.

Usage

import { AsyncParser } from '@json2csv/whatwg';

const opts = {};
const asyncOpts = {};
const writableStrategy = {};
const readableStrategy = {};
const parser = new AsyncParser(opts, asyncOpts, writableStrategy, readableStrategy);

const response = await fetch('./my-file.json');

await response.body.pipeThrough(parser).pipeTo(writableStream);

// The parse method return the stream transform readable side.
// So data can be passed to a writable stream (a file, http request, etc.)
parser.parse(data).pipeTo(writableStream);

Parameters

Options

• ndjson <Boolean> indicates that the data is in NDJSON format. Only effective when using the streaming API and not in object mode.
• fields <DataSelector[]> Defaults to toplevel JSON attributes.
• transforms <Transform[]> Array of transforms to apply to the data. A transform is a function that receives a data recod and returns a transformed record. Transforms are executed in order.
• formatters <Formatters> Object where the each key is a Javascript data type and its associated value is a formatters for the given type.
• defaultValue <Any> value to use when missing data. Defaults to <empty> if not specified. (Overridden by fields[].default)
• delimiter <String> delimiter of columns. Defaults to , if not specified.
• eol <String> overrides the default OS line ending (i.e. \n on Unix and \r\n on Windows).
• header <Boolean> determines whether or not CSV file will contain a title column. Defaults to true if not specified.
• includeEmptyRows <Boolean> includes empty rows. Defaults to false.
• withBOM <Boolean> with BOM character. Defaults to false.

Async Options

Options used by the underlying parsing library to process the binary or text stream. Not relevant when running in objectMode. Buffering is only relevant if you expect very large strings/numbers in your JSON. See @streamparser/json for more details about buffering.

• stringBufferSize <number> Size of the buffer used to parse strings. Defaults to 0 which means to don't buffer. Min valid value is 4.
• numberBufferSize <number> Size of the buffer used to parse numbers. Defaults to 0 to don't buffer.

Writable Strategy

An object that optionally defines a queuing strategy for the stream. See Writable Strategy in MDN for more details.

• highWaterMark <number> A non-negative integer. This defines the total number of chunks that can be contained in the internal queue before backpressure is applied.
• size (chunk) => {} A method containing a parameter chunk. This indicates the size to use for each chunk, in bytes.

Readable Strategy

An object that optionally defines a queuing strategy for the stream. See Readable Strategy in MDN for more details.

• highWaterMark <number> A non-negative integer. This defines the total number of chunks that can be contained in the internal queue before backpressure is applied.
• size (chunk) => {} A method containing a parameter chunk. This indicates the size to use for each chunk, in bytes.

Complete Documentation

See https://juanjodiaz.github.io/json2csv/#/parsers/whatwg-async-parser.

License

See LICENSE.md.