typescript-json-schema

What is typescript-json-schema?

The typescript-json-schema npm package is a tool that generates JSON schemas from your TypeScript types. This can be particularly useful for validating JSON data, generating documentation, or ensuring consistency between your TypeScript code and JSON data structures.

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

Generate JSON Schema from TypeScript Interface

This feature allows you to generate a JSON schema from a TypeScript interface. The code sample demonstrates how to set up the schema generator, specify the TypeScript file, and generate the schema for a specific interface.

const TJS = require('typescript-json-schema');

// Settings for the schema generator
const settings = {
  required: true
};

// Path to the TypeScript file
const files = ["./example.ts"];

// Generate the schema
const program = TJS.getProgramFromFiles(files);
const schema = TJS.generateSchema(program, "MyInterface", settings);

console.log(JSON.stringify(schema, null, 2));

Generate JSON Schema with Custom Settings

This feature allows you to customize the settings for the JSON schema generation. The code sample demonstrates how to use custom settings such as `noExtraProps` and `propOrder` to control the schema generation process.

const TJS = require('typescript-json-schema');

// Custom settings for the schema generator
const settings = {
  required: true,
  noExtraProps: true,
  propOrder: true
};

// Path to the TypeScript file
const files = ["./example.ts"];

// Generate the schema
const program = TJS.getProgramFromFiles(files);
const schema = TJS.generateSchema(program, "MyInterface", settings);

console.log(JSON.stringify(schema, null, 2));

Generate JSON Schema for Multiple Interfaces

This feature allows you to generate JSON schemas for multiple TypeScript interfaces at once. The code sample demonstrates how to specify multiple interfaces and generate their schemas in a single operation.

const TJS = require('typescript-json-schema');

// Settings for the schema generator
const settings = {
  required: true
};

// Path to the TypeScript file
const files = ["./example.ts"];

// Generate the schema
const program = TJS.getProgramFromFiles(files);
const schema = TJS.generateSchema(program, ["MyInterface1", "MyInterface2"], settings);

console.log(JSON.stringify(schema, null, 2));

Other packages similar to typescript-json-schema

typescript-to-json-schema

The typescript-to-json-schema package is another tool for generating JSON schemas from TypeScript types. It offers similar functionality to typescript-json-schema but with a different API and potentially different performance characteristics.

ts-json-schema-generator

The ts-json-schema-generator package is designed to generate JSON schemas from TypeScript types with a focus on simplicity and ease of use. It provides a straightforward API and is often used for quick schema generation tasks.

json-schema-to-typescript

The json-schema-to-typescript package works in the opposite direction, generating TypeScript types from JSON schemas. This can be useful for ensuring that your TypeScript code matches a given JSON schema, providing a complementary tool to typescript-json-schema.

README

typescript-json-schema

Generate json-schemas from your Typescript sources.

Features

• Compiles your Typescript program to get complete type information.
• Translates required properties, extends, annotation keywords, property initializers as defaults. You can find examples for these features in the api doc or the test examples.

Usage

Command line

• Install with npm install typescript-json-schema -g
• Generate schema from a typescript type: typescript-json-schema project/directory/tsconfig.json TYPE

To generate files for only some types in tsconfig.json specify filenames or globs with the --include option. This is especially useful for large projects.

In case no tsconfig.json is available for your project, you can directly specify the .ts files (this in this case we use some built-in compiler presets):

• Generate schema from a typescript type: typescript-json-schema "project/directory/**/*.ts" TYPE

The TYPE can either be a single, fully qualified type or "*" to generate the schema for all types.

Usage: typescript-json-schema <path-to-typescript-files-or-tsconfig> <type>

Options:
  --refs                Create shared ref definitions.                               [boolean] [default: true]
  --aliasRefs           Create shared ref definitions for the type aliases.          [boolean] [default: false]
  --topRef              Create a top-level ref definition.                           [boolean] [default: false]
  --titles              Creates titles in the output schema.                         [boolean] [default: false]
  --defaultProps        Create default properties definitions.                       [boolean] [default: false]
  --noExtraProps        Disable additional properties in objects by default.         [boolean] [default: false]
  --propOrder           Create property order definitions.                           [boolean] [default: false]
  --required            Create required array for non-optional properties.           [boolean] [default: false]
  --strictNullChecks    Make values non-nullable by default.                         [boolean] [default: false]
  --esModuleInterop     Use esModuleInterop when loading typescript modules.         [boolean] [default: false]
  --skipLibCheck        Use skipLibCheck when loading typescript modules.            [boolean] [default: false]
  --useTypeOfKeyword    Use `typeOf` keyword (https://goo.gl/DC6sni) for functions.  [boolean] [default: false]
  --out, -o             The output file, defaults to using stdout
  --validationKeywords  Provide additional validation keywords to include            [array]   [default: []]
  --include             Further limit tsconfig to include only matching files        [array]   [default: []]
  --ignoreErrors        Generate even if the program has errors.                     [boolean] [default: false]
  --excludePrivate      Exclude private members from the schema                      [boolean] [default: false]
  --uniqueNames         Use unique names for type symbols.                           [boolean] [default: false]
  --rejectDateType      Rejects Date fields in type definitions.                     [boolean] [default: false]
  --id                  Set schema id.                                               [string]  [default: ""]
  --defaultNumberType   Default number type.                                         [choices: "number", "integer"] [default: "number"]
  --tsNodeRegister      Use ts-node/register (needed for require typescript files).  [boolean] [default: false]
  --constAsEnum         Use enums with a single value when declaring constants.      [boolean] [default: false]
  --experimentalDecorators  Use experimentalDecorators when loading typescript modules.
   [boolean] [default: true]

Programmatic use

import { resolve } from "path";

import * as TJS from "typescript-json-schema";

// optionally pass argument to schema generator
const settings: TJS.PartialArgs = {
    required: true,
};

// optionally pass ts compiler options
const compilerOptions: TJS.CompilerOptions = {
    strictNullChecks: true,
};

// optionally pass a base path
const basePath = "./my-dir";

const program = TJS.getProgramFromFiles(
  [resolve("my-file.ts")],
  compilerOptions,
  basePath
);

// We can either get the schema for one file and one type...
const schema = TJS.generateSchema(program, "MyType", settings);

// ... or a generator that lets us incrementally get more schemas

const generator = TJS.buildGenerator(program, settings);

// generator can be also reused to speed up generating the schema if usecase allows:
const schemaWithReusedGenerator = TJS.generateSchema(program, "MyType", settings, [], generator);

// all symbols
const symbols = generator.getUserSymbols();

// Get symbols for different types from generator.
generator.getSchemaForSymbol("MyType");
generator.getSchemaForSymbol("AnotherType");

// In larger projects type names may not be unique,
// while unique names may be enabled.
const settings: TJS.PartialArgs = {
    uniqueNames: true,
};

const generator = TJS.buildGenerator(program, settings);

// A list of all types of a given name can then be retrieved.
const symbolList = generator.getSymbols("MyType");

// Choose the appropriate type, and continue with the symbol's unique name.
generator.getSchemaForSymbol(symbolList[1].name);

// Also it is possible to get a list of all symbols.
const fullSymbolList = generator.getSymbols();

getSymbols('<SymbolName>') and getSymbols() return an array of SymbolRef, which is of the following format:

type SymbolRef = {
    name: string;
    typeName: string;
    fullyQualifiedName: string;
    symbol: ts.Symbol;
};

getUserSymbols and getMainFileSymbols return an array of string.

Annotations

The schema generator converts annotations to JSON schema properties.

For example

export interface Shape {
    /**
     * The size of the shape.
     *
     * @minimum 0
     * @TJS-type integer
     */
    size: number;
}

will be translated to

{
    "$ref": "#/definitions/Shape",
    "$schema": "http://json-schema.org/draft-07/schema#",
    "definitions": {
        "Shape": {
            "properties": {
                "size": {
                    "description": "The size of the shape.",
                    "minimum": 0,
                    "type": "integer"
                }
            },
            "type": "object"
        }
    }
}

Note that we needed to use @TJS-type instead of just @type because of an issue with the typescript compiler.

You can also override the type of array items, either listing each field in its own annotation or one annotation with the full JSON of the spec (for special cases). This replaces the item types that would have been inferred from the TypeScript type of the array elements.

Example:

export interface ShapesData {
    /**
     * Specify individual fields in items.
     *
     * @items.type integer
     * @items.minimum 0
     */
    sizes: number[];

    /**
     * Or specify a JSON spec:
     *
     * @items {"type":"string","format":"email"}
     */
    emails: string[];
}

Translation:

{
    "$ref": "#/definitions/ShapesData",
    "$schema": "http://json-schema.org/draft-07/schema#",
    "definitions": {
        "Shape": {
            "properties": {
                "sizes": {
                    "description": "Specify individual fields in items.",
                    "items": {
                        "minimum": 0,
                        "type": "integer"
                    },
                    "type": "array"
                },
                "emails": {
                    "description": "Or specify a JSON spec:",
                    "items": {
                        "format": "email",
                        "type": "string"
                    },
                    "type": "array"
                }
            },
            "type": "object"
        }
    }
}

This same syntax can be used for contains and additionalProperties.

integer type alias

If you create a type alias integer for number it will be mapped to the integer type in the generated JSON schema.

Example:

type integer = number;
interface MyObject {
    n: integer;
}

Note: this feature doesn't work for generic types & array types, it mainly works in very simple cases.

require a variable from a file

(for requiring typescript files is needed to set argument tsNodeRegister to true)

When you want to import for example an object or an array into your property defined in annotation, you can use require.

Example:

export interface InnerData {
    age: number;
    name: string;
    free: boolean;
}

export interface UserData {
    /**
     * Specify required object
     *
     * @examples require("./example.ts").example
     */
    data: InnerData;
}

file example.ts

export const example: InnerData[] = [{
  age: 30,
  name: "Ben",
  free: false
}]

Translation:

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "properties": {
        "data": {
            "description": "Specify required object",
            "examples": [
                {
                    "age": 30,
                    "name": "Ben",
                    "free": false
                }
            ],
            "type": "object",
            "properties": {
                "age": { "type": "number" },
                "name": { "type": "string" },
                "free": { "type": "boolean" }
            },
            "required": ["age", "free", "name"]
        }
    },
    "required": ["data"],
    "type": "object"
}

Also you can use require(".").example, which will try to find exported variable with name 'example' in current file. Or you can use require("./someFile.ts"), which will try to use default exported variable from 'someFile.ts'.

Note: For examples a required variable must be an array.

Background

Inspired and builds upon Typson, but typescript-json-schema is compatible with more recent Typescript versions. Also, since it uses the Typescript compiler internally, more advanced scenarios are possible. If you are looking for a library that uses the AST instead of the type hierarchy and therefore better support for type aliases, have a look at vega/ts-json-schema-generator.

Debugging

npm run debug -- test/programs/type-alias-single/main.ts --aliasRefs true MyString

And connect via the debugger protocol.