@hyperjump/json-schema
Advanced tools
A JSON Schema validator with support for custom keywords, vocabularies, and dialects
A collection of modules for working with JSON Schemas.
Includes support for node.js (ES Modules, TypeScript) and browsers.
npm install @hyperjump/json-schema
When in a browser context, this library 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
})
]
The API for this library is divided into two categories: Stable and Experimental. The Stable API strictly follows semantic versioning, but the Experimental API may have backward-incompatible changes between minor versions.
All experimental features are segregated into exports that include the word "experimental" so you never accidentally depend on something that could change or be removed in future releases.
This library supports many versions of JSON Schema. Use the pattern
@hyperjump/json-schema/* to import the version you need.
import { addSchema, validate } from "@hyperjump/json-schema/draft-2020-12";
You can import support for additional versions as needed.
import { addSchema, validate } from "@hyperjump/json-schema/draft-2020-12";
import "@hyperjump/json-schema/draft-07";
Note: The default export (@hyperjump/json-schema) is reserved for the
stable version of JSON Schema that will hopefully be released in 2023.
Validate schema from JavaScript
addSchema({
$schema: "https://json-schema.org/draft/2020-12/schema",
type: "string"
}, "http://example.com/schemas/string");
const output = await validate("http://example.com/schemas/string", "foo");
if (output.valid) {
console.log("Instance is valid :-)");
} else {
console.log("Instance is invalid :-(");
}
Compile schema
If you need to validate multiple instances against the same schema, you can compile the schema into a reusable validation function.
const isString = await validate("http://example.com/schemas/string");
const output1 = isString("foo");
const output2 = isString(42);
Fetching schemas
You can fetch schemas from the web or from the file system, but when fetching from the file system, there are limitations for security reasons. If your schema has an identifier with an http(s) scheme (https://example.com), it's not allowed to reference schemas with a file scheme (file:///path/to/my/schemas).
const output = await validate("http://example.com/schemas/string", "foo");
const output = await validate(`file://${__dirname}/string.schema.json`, "foo");
Media type plugins
There is 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.
import { addMediaTypePlugin, validate } from "@hyperjump/json-schema/draft-2020-12";
import YAML from "yaml";
// Add support for JSON Schemas written in YAML
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 isString = await validate("http://example.com/schemas/string");
// Example: Fetch from file with JSON Schema YAML file extension
const isString = await validate(`file://${__dirname}/string.schema.yaml`);
// Then validate against your schema like normal
const output = isString("foo");
OpenAPI
The OpenAPI 3.0 and 3.1 meta-schemas are pre-loaded and the OpenAPI JSON Schema
dialects for each of those versions is supported. A document with a Content-Type
of application/openapi+json (web) or a file extension of openapi.json
(filesystem) is understood as an OpenAPI document.
Use the pattern @hyperjump/json-schema/* to import the version you need. The
available versions are openapi-3-0 for 3.0 and openapi-3-1 for 3.1.
YAML support isn't built in, but you can add it by writing a MediaTypePlugin.
You can use the one at lib/openapi.js as an example and replacing the JSON
parts with YAML.
import { addSchema, validate } from "@hyperjump/json-schema/openapi-3-1";
// Validate an OpenAPI document
const output = await validate("https://spec.openapis.org/oas/3.1/schema-base", openapi);
// Validate an instance against a schema in an OpenAPI document
const output = await validate(`file://${__dirname}/example.openapi.json#/components/schemas/foo`, 42);
These are available from any of the exports that refer to a version of JSON
Schema, such as @hyperjump/json-schema/draft-2020-12.
addSchema: (schema: object, retrievalUri?: string, defaultDialectId?: string) => void
Load a schema manually rather than fetching it from the filesystem or over the network.
validate: (schemaURI: string, instance: any, outputFormat: OutputFormat = FLAG) => Promise
Validate an instance against a schema. This function is curried to allow compiling the schema once and applying it to multiple instances.
validate: (schemaURI: string) => Promise<(instance: any, outputFormat: OutputFormat = FLAG) => OutputUnit>
Compiling a schema to a validation function.
FLAG: "FLAG"
An identifier for the FLAG output format as defined by the 2019-09 and
2020-12 specifications.
InvalidSchemaError: Error & { output: OutputUnit }
This error is thrown if the schema being compiled is found to be invalid.
The output field contains an OutputUnit with information about the
error. You can use the setMetaSchemaOutputFormat configuration to set the
output format that is returned in output.
setMetaSchemaOutputFormat: (outputFormat: OutputFormat) => void
Set the output format used for validating schemas.
getMetaSchemaOutputFormat: () => OutputFormat
Get the output format used for validating schemas.
setShouldMetaValidate: (isEnabled: boolean) => void
Enable or disable validating schemas.
getShouldMetaValidate: (isEnabled: boolean) => void
Determine if validating schemas is enabled.
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.
Type Definitions
The following types are used in the above definitions
OutputFormat: FLAG
Only the FLAG output format is part of the Stable API. Additional output
formats are included as part of the Experimental API.
OutputUnit: { valid: boolean }
Output is an experimental feature of the JSON Schema specification. There
may be additional fields present in the OutputUnit, but only the valid
property should be considered part of the Stable API.
MediaTypePlugin: object
parse: (response: Response, mediaTypeParameters: object) => [object | boolean, 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.
quality (optional): string
The registered media type plugins are used to create the Accept header
for HTTP requests. This property allows you to specify a quality value for
your media type. A quality value
is a string representation of a number between 0 and 1 with up to three
digits.
You can bundle schemas with external references into a single deliverable using the official JSON Schema bundling process introduced in the 2020-12 specification. Given a schema with external references, any external schemas will be embedded in the schema resulting in a Compound Schema Document with all the schemas necessary to evaluate the given schema in a single JSON document.
The bundling process allows schemas to be embedded without needing to modify any references which means you get the same output details whether you validate the bundle or the original unbundled schemas.
import { addSchema } from "@hyperjump/json-schema/draft-2020-12";
import { bundle } from "@hyperjump/json-schema/bundle";
addSchema({
"$id": "https://example.com/main"
"$schema": "https://json-schema.org/draft/2020-12/schema",
"type": "object",
"properties": {
"foo": { "$ref": "/string" }
}
});
addSchema({
"$id": "https://example.com/string",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"type": "string"
});
const bundledSchema = await bundle("https://example.com/main"); // {
// "$id": "https://example.com/main",
// "$schema": "https://json-schema.org/draft/2020-12/schema",
//
// "type": "object",
// "properties": {
// "foo": { "$ref": "/string" }
// },
//
// "$defs": {
// "https://example.com/main": {
// "$id": "https://example.com/main",
// "type": "string"
// }
// }
// }
These are available from the @hyperjump/json-schema/bundle export.
bundle: (uri: string, options: Options) => Promise
Create a bundled schema starting with the given schema. External schemas will be fetched from the filesystem, the network, or internally as needed.
Options:
$defs. When using
"full" mode, it will keep the already embedded schemas around, which will
result in some embedded schema duplication.Change the validation output format
The FLAG output format isn't very informative. You can change the output
format used for validation to get more information about failures.
import { BASIC } from "@hyperjump/json-schema/experimental";
const output = await validate("https://example.com/schema1", 42, BASIC);
Change the schema validation output format
The output format used for validating schemas can be changed as well.
import { validate, setMetaSchemaOutputFormat } from "@hyperjump/json-schema/draft-2020-12";
import { BASIC } from "@hyperjump/json-schema/experimental";
setMetaSchemaOutputFormat(BASIC);
try {
const output = await validate("https://example.com/invalid-schema");
} catch (error) {
console.log(error.output);
}
Type Definitions
OutputFormat: FLAG | BASIC | DETAILED | VERBOSE
In addition to the FLAG output format in the Stable API, the Experimental
API includes support for the BASIC, DETAILED, and VERBOSE formats as
specified in the 2019-09 specification (with some minor customizations).
This implementation doesn't include annotations or human readable error
messages. The output can be processed to create human readable error
messages as needed.
In order to create and use a custom keyword, you need to define your keyword's behavior, create a vocabulary that includes that keyword, and then create a dialect that includes your vocabulary.
import { addSchema, validate } from "@hyperjump/json-schema/draft-2020-12";
import { addKeyword, defineVocabulary, Validation } from "@hyperjump/json-schema/experimental";
import * as Schema from "@hyperjump/json-schema/schema/experimental";
// Define a keyword that's an array of schemas that are applied sequentially
// using implication: A -> B -> C -> D
addKeyword({
id: "https://example.com/keyword/implication",
compile: (schema, ast) => {
return Schema.map(async (itemSchema) => Validation.compile(await itemSchema, ast), schema);
},
interpret: (implies, instance, ast, dynamicAnchors, quiet) => {
return implies.reduce((acc, schema) => {
return !acc || Validation.interpret(schema, instance, ast, dynamicAnchors, quiet);
}, true);
}
});
// Create a vocabulary with this keyword and call it "implies"
defineVocabulary("https://example.com/vocab/logic", {
"implies": "https://example.com/keyword/implication"
});
// Create a vocabulary schema for this vocabulary
addSchema({
"$id": "https://example.com/meta/logic",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$dynamicAnchor": "meta",
"properties": {
"implies": {
"type": "array",
"items": { "$dynamicRef": "meta" },
"minItems": 2
}
}
});
// Create a dialect schema adding this vocabulary to the standard JSON Schema
// vocabularies
addSchema({
"$id": "https://example.com/dialect/logic",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$vocabulary": {
"https://json-schema.org/vocab/core": true,
"https://json-schema.org/vocab/applicator": true,
"https://json-schema.org/vocab/unevaluated": true,
"https://json-schema.org/vocab/validation": true,
"https://json-schema.org/vocab/meta-data": true,
"https://json-schema.org/vocab/format-annotation": true,
"https://json-schema.org/vocab/content": true,
"https://example.com/vocab/logic": true
},
"$dynamicAnchor": "meta",
"allOf": [
{ "$ref": "https://json-schema.org/draft/2020-12/schema" },
{ "$ref": "/meta/logic" }
]
});
// Use your dialect to validate a JSON instance
addSchema({
"$schema": "https://example.com/dialect/logic",
"type": "number",
"implies": [
{ "minimum": 10 },
{ "multipleOf": 2 }
]
}, "https://example.com/schema1");
const output = await validate("https://example.com/schema1", 42);
Custom Meta Schema
You can use a custom meta-schema to restrict users to a subset of JSON Schema functionality. This example requires that no unknown keywords are used in the schema.
addSchema({
"$id": "https://example.com/meta-schema1",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$vocabulary": {
"https://json-schema.org/draft/2020-12/vocab/core": true,
"https://json-schema.org/draft/2020-12/vocab/applicator": true,
"https://json-schema.org/draft/2020-12/vocab/unevaluated": true,
"https://json-schema.org/draft/2020-12/vocab/validation": true,
"https://json-schema.org/draft/2020-12/vocab/meta-data": true,
"https://json-schema.org/draft/2020-12/vocab/format-annotation": true,
"https://json-schema.org/draft/2020-12/vocab/content": true
},
"$dynamicAnchor": "meta",
"$ref": "https://json-schema.org/draft/2020-12/schema",
"unevaluatedProperties": false
});
addSchema({
$schema: "https://example.com/meta-schema1",
type: "number",
foo: 42
}, "https://example.com/schema1");
const output = await validate("https://example.com/schema1", 42); // Expect InvalidSchemaError
These are available from the @hyperjump/json-schema/experimental export.
addKeyword: (keywordHandler: Keyword) => void
Define a keyword for use in a vocabulary.
defineVocabulary: (id: string, keywords: { [keyword: string]: string }) => void
Define a vocabulary that maps keyword name to keyword URIs defined using
addKeyword.
getKeyword: (keywordId: string) => Keyword
Get a keyword object by its URI. This is useful for building non-validation tooling.
getKeywordName: (dialectId: string, keywordId: string) => string
Determine a keyword's name given its URI a dialect URI. This is useful when
defining a keyword that depends on the value of another keyword (such as how
contains depends on minContains and maxContains).
loadDialect: (dialectId: string, dialect: { [vocabularyId: string] }) => void
Define a dialect. In most cases, dialects are loaded automatically from the
$vocabulary keyword in the meta-schema. The only time you would need to
load a dialect manually is if you're creating a distinct version of JSON
Schema rather than creating a dialect of an existing version of JSON Schema.
Validation: Keyword
A Keyword object that represents a "validate" operation. You would use this for compiling and evaluating sub-schemas when defining a custom keyword.
Keyword: object
id: string
A URI that uniquely identifies the keyword. It should use a domain you own to avoid conflict with keywords defined by others.
compile: (schema: SchemaDocument, ast: AST, parentSchema: SchemaDocument) => Promise
This function takes the keyword value, does whatever preprocessing it
can on it without an instance, and returns the result. The returned
value will be passed to the interpret function. The ast parameter is
needed for compiling sub-schemas. The parentSchema parameter is
primarily useful for looking up the value of an adjacent keyword that
might effect this one.
interpret: (compiledKeywordValue: A, instance: JsonDocument, ast: AST, dynamicAnchors: Anchors, quiet: boolean) => boolean
This function takes the value returned by the compile function and the
instance value that is being validated and returns whether the value is
valid or not. The other parameters are only needed for validating
sub-schemas.
collectEvaluatedProperties?: (compiledKeywordValue: A, instance: JsonDocument, ast: AST, dynamicAnchors: Anchors) => string[] | false
If the keyword is an applicator, it will need to implements this
function for unevaluatedProperties to work as expected.
collectEvaluatedItems?: (compiledKeywordValue: A, instance: JsonDocument, ast: AST, dynamicAnchors: Anchors) => Set | false
If the keyword is an applicator, it will need to implements this
function for unevaluatedItems to work as expected.
These functions are available from the
@hyperjump/json-schema/schema/experimental export.
This library uses SchemaDocument objects to represent a value in a schema. You'll work with these objects if you create a custom keyword. This module is a set of functions for working with SchemaDocuments.
Schema.add: (schema: object, retrievalUri?: string, dialectId?: string) => string
Load a schema. Returns the identifier for the schema.
Schema.get: (url: string, contextDoc?: SchemaDocument) => Promise
Fetch a schema. Schemas can come from an HTTP request, a file, or a schema
that was added with Schema.add.
Schema.uri: (doc: SchemaDocument) => string
Returns a URI for the value the SchemaDocument represents.
Schema.value: (doc: SchemaDocument) => any
Returns the value the SchemaDocument represents.
Schema.typeOf: (doc: SchemaDocument, type: string) => boolean
Determines if the JSON type of the given doc matches the given type.
Schema.has: (key: string, doc: SchemaDocument) => Promise
Similar to key in schema.
Schema.step: (key: string, doc: SchemaDocument) => Promise
Similar to schema[key], but returns an SchemaDocument.
Schema.entries: (doc: SchemaDocument) => Promise<[[string, SchemaDocument]]>
Similar to Object.entries, but returns SchemaDocuments for values.
Schema.keys: (doc: SchemaDocument) => [string]
Similar to Object.keys.
Schema.map: (fn: (item: Promise, index: integer) => T, doc: SchemaDocument) => Promise<[T]>
A map function for an SchemaDocument whose value is an array.
Schema.length: (doc: SchemaDocument) => number
Similar to Array.prototype.length.
Schema.toSchema: (doc: SchemaDocument, options: ToSchemaOptions) => object
Get a raw schema from a Schema Document.
Type Definitions
The following types are used in the above definitions
ToSchemaOptions: object
file:// URIs will be generated
relative to this path.$schema keyword will be omitted.These functions are available from the
@hyperjump/json-schema/instance/experimental export.
This library uses InstanceDocument objects to represent a value in an instance. You'll work with these objects if you create a custom keyword. This module is a set of functions for working with InstanceDocuments.
Instance.cons: (instance: any, uri?: string) => InstanceDocument
Construct an InstanceDocument from a value.
Instance.get: (url: string, contextDoc: InstanceDocument) => InstanceDocument
Apply a same-resource reference to a InstanceDocument.
Instance.uri: (doc: InstanceDocument) => string
Returns a URI for the value the InstanceDocument represents.
Instance.value: (doc: InstanceDocument) => any
Returns the value the InstanceDocument represents.
Instance.has: (key: string, doc: InstanceDocument) => any
Similar to key in instance.
Instance.typeOf: (doc: InstanceDocument, type: string) => boolean
Determines if the JSON type of the given doc matches the given type.
Instance.step: (key: string, doc: InstanceDocument) => InstanceDocument
Similar to schema[key], but returns a InstanceDocument.
Instance.entries: (doc: InstanceDocument) => [string, InstanceDocument]
Similar to Object.entries, but returns IDocs for values.
Instance.keys: (doc: InstanceDocument) => [string]
Similar to Object.keys.
Instance.map: (fn: (item: InstanceDocument, index: integer) => T, doc: InstanceDocument) => [T]
A map function for an InstanceDocument whose value is an array.
Instance.reduce: (fn: (accumulator: T, item: InstanceDocument, index: integer) => T, initial: T, doc: InstanceDocument) => T
A reduce function for an InstanceDocument whose value is an array.
Instance.every: (fn: (doc: InstanceDocument, index: integer) => boolean, doc: InstanceDocument) => boolean
An every function for an InstanceDocument whose value is an array.
Instance.some: (fn: (doc: InstanceDocument, index: integer) => boolean, doc: InstanceDocument) => boolean
A some function for an InstanceDocument whose value is an array.
Instance.length: (doc: InstanceDocument) => number
Similar to Array.prototype.length.
JSON Schema is for annotating JSON instances as well as validating them. This module provides utilities for working with JSON documents annotated with JSON Schema.
An annotated JSON document is represented as an AnnotatedInstance object. This object is a wrapper around your JSON document with functions that allow you to traverse the data structure and get annotations for the values within.
import { annotate, annotatedWith, addSchema } from "@hyperjump/json-schema/annotations/experimental";
import * as AnnotatedInstance from "@hyperjump/json-schema/annotated-instance/experimental";
const schemaId = "https://example.com/foo";
const dialectId = "https://json-schema.org/draft/2020-12/schema";
addSchema({
"$schema": dialectId,
"title": "Person",
"unknown": "foo",
"type": "object",
"properties": {
"name": {
"$ref": "#/$defs/name",
"deprecated": true
},
"givenName": {
"$ref": "#/$defs/name",
"title": "Given Name"
},
"familyName": {
"$ref": "#/$defs/name",
"title": "Family Name"
}
},
"$defs": {
"name": {
"type": "string",
"title": "Name"
}
}
}, schemaId);
const instance = await annotate(schemaId, {
name: "Jason Desrosiers",
givenName: "Jason",
familyName: "Desrosiers"
});
// Get the title of the instance
const titles = AnnotatedInstance.annotation(instance, "title", dialectId); // => ["Person"]
// Unknown keywords are collected as annotations
const unknowns = AnnotatedInstance.annotation(instance, "unknown", dialectId); // => ["foo"]
// The type keyword doesn't produce annotations
const types = AnnotatedInstance.annotation(instance, "type", dialectId); // => []
// Get the title of each of the properties in the object
AnnotatedInstance.entries(instance)
.map(([propertyName, propertyInstance]) => {
return { propertyName, titles: Instance.annotation(propertyInstance, "title", dialectId) }; // => (Example) { propertyName: "givenName", titles: ["Given Name", "Name"] });
});
// List all locations in the instance that are deprecated
for (const deprecated of AnnotatedInstance.annotatedWith(instance, "deprecated", dialectId)) {
if (AnnotatedInstance.annotation(instance, "deprecated", dialectId)[0]) {
logger.warn(`The value at '${deprecated.pointer}' has been deprecated.`); // => (Example) "WARN: The value at '/name' has been deprecated."
}
}
These are available from the @hyperjump/json-schema/annotations/experimental
export.
annotate: (schemaUri: string, instance: any, outputFormat: OutputFormat = FLAG) => Promise
Annotate an instance using the given schema. The function is curried to allow compiling the schema once and applying it to multiple instances. This may throw an InvalidSchemaError if there is a problem with the schema or a ValidationError if the instance doesn't validate against the schema.
ValidationError: output: OutputUnit -- The errors that were found while validating the instance.
These are available from the
@hyperjump/json-schema/annotated-instance/experimental export. The
following functions are available in addition to the functions available in the
Instance API.
annotation: (instance: AnnotatedInstance, keyword: string, dialectId?: string) => [any]
Get the annotations for a given keyword at the location represented by the instance object.
annotatedWith: (instance: AnnotatedInstance, keyword: string, dialectId?: string) => [AnnotatedInstance]
Get an array of instances for all the locations that are annotated with the given keyword.
annotate: (instance: AnnotatedInstance, keywordId: string, value: any) => AnnotatedInstance
Add an annotation to an instance. This is used internally, you probably don't need it.
These are available from the @hyperjump/json-schema/experimental export.
compile: (schema: SchemaDocument) => Promise
Return a compiled schema. This is useful if you're creating tooling for something other than validation.
interpret: (schema: CompiledSchema, instance: Instance, outputFormat: OutputFormat = BASIC) => OutputUnit
A curried function for validating an instance against a compiled schema. This can be useful for creating custom output formats.
Run the tests
npm test
Run the tests with a continuous test runner
npm test -- --watch
FAQs
A JSON Schema validator with support for custom keywords, vocabularies, and dialects
The npm package @hyperjump/json-schema receives a total of 38,343 weekly downloads. As such, @hyperjump/json-schema popularity was classified as popular.
We found that @hyperjump/json-schema demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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