json-schema-to-typescript

What is json-schema-to-typescript?

The json-schema-to-typescript npm package is a tool that converts JSON Schema definitions into TypeScript interfaces. This is particularly useful for ensuring type safety in TypeScript projects by generating types directly from JSON Schema, which can help in maintaining consistency between your data models and TypeScript types.

What are json-schema-to-typescript's main functionalities?

Convert JSON Schema to TypeScript Interface

This feature allows you to convert a JSON Schema into a TypeScript interface. The `compile` function takes a JSON Schema and a name for the resulting TypeScript interface, and returns a promise that resolves to the TypeScript code as a string.

const { compile } = require('json-schema-to-typescript');

const schema = {
  title: 'Example Schema',
  type: 'object',
  properties: {
    name: { type: 'string' },
    age: { type: 'number' }
  },
  required: ['name', 'age']
};

compile(schema, 'ExampleSchema')
  .then(ts => console.log(ts));

Generate TypeScript Definitions from Multiple Schemas

This feature allows you to generate TypeScript definitions from a JSON Schema file. The `compileFromFile` function reads a JSON Schema from a file and returns a promise that resolves to the TypeScript code as a string.

const { compileFromFile } = require('json-schema-to-typescript');

compileFromFile('path/to/schema.json')
  .then(ts => console.log(ts));

Customizing Output

This feature allows you to customize the output of the TypeScript definitions. The `compile` function accepts an options object where you can specify various settings like adding a banner comment to the generated TypeScript code.

const { compile } = require('json-schema-to-typescript');

const schema = {
  title: 'Example Schema',
  type: 'object',
  properties: {
    name: { type: 'string' },
    age: { type: 'number' }
  },
  required: ['name', 'age']
};

const options = {
  bannerComment: '/* This is a generated file */'
};

compile(schema, 'ExampleSchema', options)
  .then(ts => console.log(ts));

Other packages similar to json-schema-to-typescript

typescript-json-schema

The typescript-json-schema package generates JSON Schema from your TypeScript types. It works in the opposite direction compared to json-schema-to-typescript, making it useful for projects where you start with TypeScript types and need to generate JSON Schema for validation or documentation purposes.

quicktype

The quicktype package can generate TypeScript types from JSON Schema, JSON data, and other sources. It supports multiple languages and is highly configurable, making it a versatile tool for generating types from various data formats.

json-schema-to-flow-type

The json-schema-to-flow-type package converts JSON Schema to Flow types. While it serves a similar purpose to json-schema-to-typescript, it is specifically designed for projects using Flow instead of TypeScript.

README

json-schema-to-typescript

Compile JSON Schema to TypeScript typings.

Example

Check out the live demo.

Input:

{
  "title": "Example Schema",
  "type": "object",
  "properties": {
    "firstName": {
      "type": "string"
    },
    "lastName": {
      "type": "string"
    },
    "age": {
      "description": "Age in years",
      "type": "integer",
      "minimum": 0
    },
    "hairColor": {
      "enum": ["black", "brown", "blue"],
      "type": "string"
    }
  },
  "additionalProperties": false,
  "required": ["firstName", "lastName"]
}

Output:

export interface ExampleSchema {
  firstName: string;
  lastName: string;
  /**
   * Age in years
   */
  age?: number;
  hairColor?: "black" | "brown" | "blue";
}

Installation

npm install json-schema-to-typescript

Usage

json-schema-to-typescript is easy to use via the CLI, or programmatically.

CLI

First make the CLI available using one of the following options:

# install locally, then use `npx json2ts`
npm install json-schema-to-typescript

# or install globally, then use `json2ts`
npm install json-schema-to-typescript --global

# or install to npm cache, then use `npx --package=json-schema-to-typescript json2ts`
# (you don't need to run an install command first)

Then, use the CLI to convert JSON files to TypeScript typings:

cat foo.json | json2ts > foo.d.ts
# or
json2ts foo.json > foo.d.ts
# or
json2ts foo.yaml foo.d.ts
# or
json2ts --input foo.json --output foo.d.ts
# or
json2ts -i foo.json -o foo.d.ts
# or (quote globs so that your shell doesn't expand them)
json2ts -i 'schemas/**/*.json'
# or
json2ts -i schemas/ -o types/

You can pass any of the options described below (including style options) as CLI flags. Boolean values can be set to false using the no- prefix.

# generate code for definitions that aren't referenced
json2ts -i foo.json -o foo.d.ts --unreachableDefinitions
# use single quotes and disable trailing semicolons
json2ts -i foo.json -o foo.d.ts --style.singleQuote --no-style.semi

API

To invoke json-schema-to-typescript from your TypeScript or JavaScript program, import it and call compile or compileFromFile.

import { compile, compileFromFile } from 'json-schema-to-typescript'

// compile from file
compileFromFile('foo.json')
  .then(ts => fs.writeFileSync('foo.d.ts', ts))

// or, compile a JS object
let mySchema = {
  properties: [...]
}
compile(mySchema, 'MySchema')
  .then(ts => ...)

See server demo and browser demo for full examples.

Options

compileFromFile and compile accept options as their last argument (all keys are optional):

key	type	default	description
additionalProperties	boolean	true	Default value for additionalProperties, when it is not explicitly set
bannerComment	string	"/* eslint-disable */\n/**\n* This file was automatically generated by json-schema-to-typescript.\n* DO NOT MODIFY IT BY HAND. Instead, modify the source JSON Schema file,\n* and run json-schema-to-typescript to regenerate this file.\n*/"	Disclaimer comment prepended to the top of each generated file
customName	(LinkedJSONSchema, string | undefined) => string | undefined	undefined	Custom function to provide a type name for a given schema
cwd	string	process.cwd()	Root directory for resolving $refs
declareExternallyReferenced	boolean	true	Declare external schemas referenced via $ref?
enableConstEnums	boolean	true	Prepend enums with const?
inferStringEnumKeysFromValues	boolean	false	Create enums from JSON enums with eponymous keys
format	boolean	true	Format code? Set this to false to improve performance.
ignoreMinAndMaxItems	boolean	false	Ignore maxItems and minItems for array types, preventing tuples being generated.
maxItems	number	20	Maximum number of unioned tuples to emit when representing bounded-size array types, before falling back to emitting unbounded arrays. Increase this to improve precision of emitted types, decrease it to improve performance, or set it to -1 to ignore maxItems.
strictIndexSignatures	boolean	false	Append all index signatures with | undefined so that they are strictly typed.
style	object	{ bracketSpacing: false, printWidth: 120, semi: true, singleQuote: false, tabWidth: 2, trailingComma: 'none', useTabs: false }	A Prettier configuration
unknownAny	boolean	true	Use unknown instead of any where possible
unreachableDefinitions	boolean	false	Generates code for $defs that aren't referenced by the schema.
$refOptions	object	{}	$RefParser Options, used when resolving $refs

Tests

$ npm test

Features

• title => interface
• Primitive types:
  • array
  • homogeneous array
  • boolean
  • integer
  • number
  • null
  • object
  • string
  • homogeneous enum
  • heterogeneous enum
• Non/extensible interfaces
• Custom JSON-schema extensions
• Nested properties
• Schema definitions
• Schema references
• Local (filesystem) schema references
• External (network) schema references
• Add support for running in browser
• default interface name
• infer unnamed interface name from filename
• deprecated
• allOf ("intersection")
• anyOf ("union")
• oneOf (treated like anyOf)
• maxItems (eg)
• minItems (eg)
• additionalProperties of type
• patternProperties (partial support)
• extends
• required properties on objects (eg)
• validateRequired (eg)
• literal objects in enum (eg)
• referencing schema by id (eg)
• custom typescript types via tsType

Custom schema properties:

• tsType: Overrides the type that's generated from the schema. Useful for forcing a type to any or when using non-standard JSON schema extensions (eg).
• tsEnumNames: Overrides the names used for the elements in an enum. Can also be used to create string enums (eg).

Not expressible in TypeScript:

• dependencies (single, multiple)
• divisibleBy (eg)
• format (eg)
• multipleOf (eg)
• maximum (eg)
• minimum (eg)
• maxProperties (eg)
• minProperties (eg)
• not/disallow
• oneOf ("xor", use anyOf instead)
• pattern (string, regex)
• uniqueItems (eg)

FAQ

JSON-Schema-to-TypeScript is crashing on my giant file. What can I do?

Prettier is known to run slowly on really big files. To skip formatting and improve performance, set the format option to false.

Further Reading

• JSON-schema spec: https://tools.ietf.org/html/draft-zyp-json-schema-04
• JSON-schema wiki: https://github.com/json-schema/json-schema/wiki
• JSON-schema test suite: https://github.com/json-schema/JSON-Schema-Test-Suite/blob/node
• TypeScript spec: https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md

Who uses JSON-Schema-to-TypeScript?

• Alibaba
• Amazon, AWSLabs
• Expo
• FormatJS
• Microsoft
• Mozilla
• Nx
• RStudio
• Sourcegraph
• Stryker
• Webpack
• See more