csv42

csv42

A small and fast CSV parser with support for nested JSON.

Features

• 2 way: convert JSON to CSV and the other way around.
• Simple: straightforward and flexible API.
• Lightweight: 2KB gzipped with everything included, 1KB gzipped when only using json2csv.
• Fast: faster than the popular CSV libraries out there. See benchmark.
• Modular: only load what you use, thanks to ES5 modules and a plugin architecture.
• Powerful:
  • Configurable properties: header, delimiter, eol.
  • Configurable fields, with custom value getters and setters and the ability to ignore fields.
  • Configurable serialization and deserialization of values via formatValue and parseValue.
  • Support for nested JSON objects: either flatten nested contents, or stringify as a JSON object.
• Standards compliant: adheres to the CSV standard RFC 4180.
• Universal: Created for the browser, but can be used in any JavaScript environment like node.js. TypeScript types included.

Note that the parser has no streaming support.

Why?

Well, you have to write a CSV parser at least once in you life, right? ;)

The csv42 library was developed specifically for https://jsoneditoronline.org, for use in the browser. Besides being small and fast, one important feature is supporting nested JSON objects. So, why the name csv42? Just because 42 is a beautiful number and to remind us that there is a whole universe of beautiful CSV libraries out there.

Install

npm install csv42

Usage

Install the library once:

Convert JSON to CSV

import { json2csv } from 'csv42'

const users = [
  { id: 1, name: 'Joe', address: { city: 'New York', street: '1st Ave' } },
  { id: 2, name: 'Sarah', address: { city: 'Manhattan', street: 'Spring street' } }
]

// By default, nested JSON properties are flattened
const csv = json2csv(users)
console.log(csv)
// id,name,address.city,address.street
// 1,Joe,New York,1st Ave
// 2,Sarah,Manhattan,Spring street

// You can turn off flattening using the option `flatten`
const csvFlat = json2csv(users, { flatten: false })
console.log(csvFlat)
// id,name,address
// 1,Joe,"{""city"":""New York"",""street"":""1st Ave""}"
// 2,Sarah,"{""city"":""Manhattan"",""street"":""Spring street""}"

// The CSV output can be fully customized and transformed using `fields`:
const csvCustom = json2csv(users, {
  fields: [
    { name: 'name', getValue: (item) => item.name },
    { name: 'address', getValue: (item) => item.address.city + ' - ' + object.address.street }
  ]
})
console.log(csvCustom)
// name,address
// Joe,New York - 1st Ave
// Sarah,Manhattan - Spring street

Convert CSV to JSON

import { csv2json } from 'csv42'

const csv = `id,name,address.city,address.street
1,Joe,New York,1st Ave
2,Sarah,Manhattan,Spring street`

// By default, fields containing a dot will be parsed inty nested JSON objects
const users = csv2json(csv)
console.log(users)
// [
//   { id: 1, name: 'Joe', address: { city: 'New York', street: '1st Ave' } },
//   { id: 2, name: 'Sarah', address: { city: 'Manhattan', street: 'Spring street' } }
// ]

// Creating nested objects can be turned off using the option `nested`
const usersFlat = csv2json(csv, { nested: false })
console.log(usersFlat)
// [
//   { id: 1, name: 'Joe', 'address.city': 'New York', 'address.street': '1st Ave' },
//   { id: 2, name: 'Sarah', 'address.city': 'Manhattan', 'address.street': 'Spring street' }
// ]

// The JSON output can be customized using `fields`
const usersCustom = csv2json(csv, {
  fields: [
    { name: 'name', setValue: (item, value) => (item.name = value) },
    { name: 'address.city', setValue: (item, value) => (item.city = value) }
  ]
})
console.log(usersCustom)
// [
//   { name: 'Joe', city: 'New York' },
//   { name: 'Sarah', city: 'Manhattan' }
// ]

API

json2csv<T>(json: T[], options?: CsvOptions<T>) : string

Where options is an object with the following properties:

Option	Type	Description
header	boolean	If true, a header will be created as first line of the CSV.
delimiter	string	Default delimiter is ,. A delimiter must be a single character.
eol	\r\n or \n	End of line, can be \r\n (default) or \n.
flatten	boolean or (value: unknown) => boolean	If true (default), plain, nested objects will be flattened in multiple CSV columns, and arrays and classes will be serialized in a single field. When false, nested objects will be serialized as JSON in a single CSV field. This behavior can be customized by providing your own callback function for flatten. For example, to flatten objects and arrays, you can use json2csv(json, { flatten: isObjectOrArray }), and to flatten a specific class, you can use json2csv(json, { flatten: value => isObject(value) || isCustomClass(value) }). The option flattenis not applicable whenfields is defined.
fields	CsvField<T>[] or CsvFieldsParser<T>	A list with fields to be put into the CSV file. This allows specifying the order of the fields and which fields to include/excluded.
formatValue	ValueFormatter	Function used to change any type of value into a serialized string for the CSV. The build in formatter will only enclose values in quotes when necessary, and will stringify nested JSON objects.

A simple example of a ValueFormatter is the following. This formatter will enclose every value in quotes:

function formatValue(value: unknown): string {
  return '"' + String(value) + '"'
}

csv2json<T>(csv: string, options?: JsonOptions) : T[]

Where options is an object with the following properties:

Option	Type	Description
header	boolean	Should be set true when the first line of the CSV file contains a header
delimiter	string	Default delimiter is ,. A delimiter must be a single character.
nested	boolean	If true (default), field names containing a dot will be parsed into nested JSON objects. The option nested is not applicable when fields is defined.
fields	JsonField[] or JsonFieldsParser	A list with fields to be extracted from the CSV file into JSON. This allows specifying which fields are include/excluded, and how they will be put into the JSON object. A field can be specified either by name, like { name, setValue }, or by the index of the columns in the CSV file, like { index, setValue }.
parseValue	ValueParser	Used to parse a stringified value into a value again (number, boolean, string, ...). The build in parser will parse numbers and booleans, and will parse stringified JSON objects.

A simple value parser can look as follows. This will keep all values as string:

function parseValue(value: string): unknown {
  return value.startsWith('"') ? value.substring(1, value.length - 1).replaceAll('""', '"') : value
}

Utility functions

The library exports a number of utility functions:

Function	Description
createFormatValue(delimiter: string): (value: unknown) => string	Create a function that can format (stringify) a value into a valid CSV value, escaping the value when needed. This function is used as default for the option formatValue.
parseValue(value: string): unknown	Parse a string into a value, parse numbers into a number, etc. This is the function used by default for the option parseValue.
unescapeValue(value: string) : string	Unescape an escaped value like "hello ""Joe""" into the string hello "Joe".
collectNestedPaths(records: NestedObject[], recurse: boolean): Path[]	Loop over the data and collect all nested paths. This can be used to generate a list with fields.
parsePath(pathStr: string): Path	Parse a path like 'items[3].name'
stringifyPath(path: Path): string	Stringify a path into a string like 'items[3].name'
getIn(object: NestedObject, path: Path): unknown	Get a nested property from an object
setIn(object: NestedObject, path: Path, value: unknown): NestedObject	Set a nested property in an object
isObject(value: unknown): boolean	Returns true when value is a plain JavaScript object, and returns false for primitive values, arrays, and classes. Can be used as callback function for the option flatten.
isObjectOrArray(value: unknown): boolean	Returns true when value is a plain JavaScript object or array, and returns false for primitive values and classes. Can be used as callback function for the option flatten.

Alternatives

• https://www.npmjs.com/package/csv
• https://juanjodiaz.github.io/json2csv/
• https://www.npmjs.com/package/json-2-csv
• https://www.npmjs.com/package/papaparse
• https://www.npmjs.com/package/csvtojson
• https://www.npmjs.com/package/csv-stringify
• https://www.npmjs.com/package/csv-parser
• https://www.npmjs.com/package/fast-csv
• Any many many more...

Release

To release a new version:

$ npm run release

This will:

• lint
• test
• build
• increment the version number
• push the changes to git, add a git version tag
• publish the npm package

To try the build and see the change list without actually publishing:

$ npm run release-dry-run

License

csv42 is released as open source under the permissive the ISC license.

If you are using csv42 commercially, there is a social (but no legal) expectation that you help fund its maintenance. Start here.

Changelog

4.0.0 (2023-06-02)

⚠ BREAKING CHANGES

• The API is now generic, so you can use the library like json2csv<User>(...) and csv2json<User>(...). The typings of the value getters and setters (getValue and setValue) is changed, and the type of NestedObject is changed.

Features

• improved TypeScript support (fixes #2) (9ec74ae)