@hyperjump/json-schema

Hyperjump - JSON Schema Validator

JSON Schema Validator (JSV) is built on JSON Schema Core.

• Supported JSON Schema Dialects
  • draft-04 | draft-06 | draft-07 | Draft 2019-09 | Draft 2020-12
  • Create your own dialect with JSC
• Schemas can reference other schemas using a different draft
• Supported vocabularies (new in Draft 2019-09)
  • Draft 2019-09: core | applicator | validation | meta-data | content
  • Draft 2020-12: core | applicator | validation | meta-data | content | format-annotations
  • Create your own keywords and vocabularies with JSC
• Output formats
  • FLAG, BASIC, DETAILED, VERBOSE
  • Create your own output format with JSC
• Load schemas from filesystem (file://), network (http(s)://), or JavaScript
• Build non-validation JSON-Schema based tools with JSC

Install

JSV includes support for node.js JavaScript (CommonJS and ES Modules), TypeScript, and browsers.

Node.js

npm install @hyperjump/json-schema

Browser

When in a browser context, JSV is designed to use the browser's fetch implementation instead of a node.js fetch clone. The Webpack bundler does this properly without any extra configuration, but if you are using the Rollup bundler you will need to include the browser: true option in your Rollup configuration.

  plugins: [
    resolve({
      browser: true
    }),
    commonjs()
  ]

Versioning

This project is in beta and there may be breaking changes at any time. When it's stable enough, I'll publish v1.0.0 and follow semantic versioning from there on out.

Usage

const JsonSchema = require("@hyperjump/json-schema");


// Example: Inline schema
const schemaJson = {
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "http://example.com/schemas/string",
  "type": "string"
};
JsonSchema.add(schemaJson);
const schema = await JsonSchema.get("http://example.com/schemas/string");

// Example: Fetch from the web
const schema = await JsonSchema.get("http://example.com/schemas/string");

// Example: Fetch from file
const schema = await JsonSchema.get("file:///path/to/my/schemas/string.schema.json");

// Example: Validate instance
const output = await JsonSchema.validate(schema, "foo");
if (output.valid) {
  console.log("Instance is valid :-)");
} else {
  console.log("Instance is invalid :-(");
}

// Example: Precompile validator
const isString = await JsonSchema.validate(schema);
const output = isString("foo");

// Example: Specify output format
const output = await JsonSchema.validate(schema, "foo", JsonSchema.VERBOSE);

// Example: Specify meta-validation output format
JsonSchema.setMetaOutputFormat(JsonSchema.FLAG);

// Example: Disable meta-validation
JsonSchema.setShouldMetaValidate(false);

Media Types

JSV has a plugin system for adding support for different media types. By default it's configured to accept schemas that have the application/schema+json Content-Type (web) or a .schema.json file extension (filesystem). If for example, you want to fetch schemas that are written in YAML, you can add a MediaTypePlugin to support that.

• Core.addMediaTypePlugin: (contentType: string, plugin: MediaTypePlugin) => void

  Add a custom media type handler to support things like YAML or to change the way JSON is supported.

• MediaTypePlugin: object

  • parse: (response: Response, mediaTypeParameters: object) => [SchemaObject, string]

    Given a fetch Response object, parse the body of the request. Return the parsed schema and an optional default dialectId.

  • matcher: (path) => boolean

    Given a filesystem path, return whether or not the file should be considered a member of this media type.

const JsonSchema = require("@hyperjump/json-schema");
const YAML = require("yaml");


// Add support for JSON Schemas written in YAML
JsonSchema.addMediaTypePlugin("application/schema+yaml", {
  parse: async (response) => [YAML.parse(await response.text()), undefined],
  matcher: (path) => path.endsWith(".schema.yaml")
});

// Example: Fetch schema with Content-Type: application/schema+yaml from the web
const schema = await JsonSchema.get("http://example.com/schemas/string");

// Example: Fetch from file with JSON Schema YAML file extension
const schema = await JsonSchema.get("file:///path/to/my/schemas/string.schema.yaml");

// Then validate against your schema like normal

TypeScript

Although the package is written in JavaScript, type definitions are included for TypeScript support. The following example shows the types you might want to know.

import JsonSchema, { InvalidSchemaError } from "@hyperjump/json-schema";
import type { SchemaDocument, Validator, Result, Draft202012Schema } from "@hyperjump/json-schema";


const schemaJson: Draft202012Schema = {
  "$id": "https://json-schema.hyperjump.io/schema",
  "$schema": "https://json-schema.org/draft/2020-12/schema",

  "type": "string"
};
JsonSchema.add(schemaJson);

const schema: SchemaDocument = await JsonSchema.get("https://json-schema.hyperjump.io/schema");
try {
  const isString: Validator = await JsonSchema.validate(schema);
  const result: Result = isString("foo");
  console.log("isString:", result.valid);
} catch (error: unknown) {
  if (error instanceof InvalidSchemaError) {
    console.log(error.output);
  } else {
    console.log(error);
  }
}

API

• add: (schema: object, url?: URI, dialectId?: string) => SDoc

  Load a schema. See JSC - $id and JSC - $schema for more information.

• get: (url: URI, contextDoc?: SDoc, recursive: boolean = false) => Promise

  Fetch a schema. Schemas can come from an HTTP request, a file, or a schema that was added with add.

• validate: (schema: SDoc, instance: any, outputFormat: OutputFormat = FLAG) => Promise

  Validate an instance against a schema. The function is curried to allow compiling the schema once and applying it to multiple instances.

• compile: (schema: SDoc) => Promise

  Compile a schema to be interpreted later. A compiled schema is a JSON serializable structure that can be serialized an restored for later use.

• interpret: (schema: CompiledSchema, instance: any, outputFormat: OutputFormat = FLAG) => OutputUnit

  A curried function for validating an instance against a compiled schema.

• setMetaOutputFormat: (outputFormat: OutputFormat = DETAILED) => undefined

  Set the output format for meta-validation. Meta-validation output is only returned if meta-validation results in an error.

• setShouldMetaValidate: (isEnabled: boolean) => undefined

  Enable or disable meta-validation.

• OutputFormat: [FLAG | BASIC | DETAILED | VERBOSE]

  See JSC - Output for more information on output formats.

Not (yet) Supported

This implementation supports all required features of JSON Schema. The following optional features are not supported yet.

• The format-assertion vocabulary

Contributing

Tests

Run the tests

npm test

Run the tests with a continuous test runner

npm test -- --watch