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jsonld.js

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Introduction

This library is an implementation of the JSON-LD specification in JavaScript.

JSON, as specified in RFC7159, is a simple language for representing objects on the Web. Linked Data is a way of describing content across different documents or Web sites. Web resources are described using IRIs, and typically are dereferencable entities that may be used to find more information, creating a "Web of Knowledge". JSON-LD is intended to be a simple publishing method for expressing not only Linked Data in JSON, but for adding semantics to existing JSON.

JSON-LD is designed as a light-weight syntax that can be used to express Linked Data. It is primarily intended to be a way to express Linked Data in JavaScript and other Web-based programming environments. It is also useful when building interoperable Web Services and when storing Linked Data in JSON-based document storage engines. It is practical and designed to be as simple as possible, utilizing the large number of JSON parsers and existing code that is in use today. It is designed to be able to express key-value pairs, RDF data, RDFa data, Microformats data, and Microdata. That is, it supports every major Web-based structured data model in use today.

The syntax does not require many applications to change their JSON, but easily add meaning by adding context in a way that is either in-band or out-of-band. The syntax is designed to not disturb already deployed systems running on JSON, but provide a smooth migration path from JSON to JSON with added semantics. Finally, the format is intended to be fast to parse, fast to generate, stream-based and document-based processing compatible, and require a very small memory footprint in order to operate.

Conformance

This library aims to conform with the following:

The JSON-LD Working Group is now developing JSON-LD 1.1. Library updates to conform with newer specifications will happen as features stabilize and development time and resources permit.

The test runner is often updated to note or skip newer tests that are not yet supported.

Installation

Node.js + npm

npm install jsonld

const jsonld = require('jsonld');

Browser (bundler) + npm

npm install jsonld

Use your favorite bundling technology (webpack, Rollup, etc) to directly bundle your code that loads jsonld. Note that you will need support for ES2017+ code.

Browser Bundles

The built npm package includes bundled code suitable for use in browsers. Two versions are provided:

  • ./dist/jsonld.min.js: A version built for wide compatibility with modern and older browsers. Includes many polyfills and code transformations and is larger and less efficient.
  • ./dist/jsonld.esm.min.js: A version built for features available in browsers that support ES Modules. Fewer polyfills and transformations are required making the code smaller and more efficient.

The two bundles can be used at the same to to allow modern browsers to use newer code. Lookup using script tags with type="module" and nomodule.

Also see the webpack.config.js if you would like to make a custom bundle for specific targets.

Browser (AMD) + npm

npm install jsonld

Use your favorite technology to load node_modules/dist/jsonld.min.js.

CDNJS CDN

To use CDNJS include this script tag:

<script src="https://cdnjs.cloudflare.com/ajax/libs/jsonld/1.0.0/jsonld.min.js"></script>

Check https://cdnjs.com/libraries/jsonld for the latest available version.

jsDeliver CDN

To use jsDeliver include this script tag:

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/jsonld.min.js"></script>

See https://www.jsdelivr.com/package/npm/jsonld for the latest available version.

unpkg CDN

To use unpkg include this script tag:

<script src="https://unpkg.com/[email protected]/dist/jsonld.min.js"></script>

See https://unpkg.com/jsonld/ for the latest available version.

JSPM

jspm install npm:jsonld

import * as jsonld from 'jsonld';
// or
import {promises} from 'jsonld';
// or
import {JsonLdProcessor} from 'jsonld';

Node.js native canonize bindings

For specialized use cases there is an optional rdf-canonize-native package available which provides a native implementation for canonize(). It is used by installing the package and setting the useNative option of canonize() to true. Before using this mode it is highly recommended to run benchmarks since the JavaScript implementation is often faster and the bindings add toolchain complexity.

npm install jsonld
npm install rdf-canonize-native

Examples

Example data and context used throughout examples below:

const doc = {
  "http://schema.org/name": "Manu Sporny",
  "http://schema.org/url": {"@id": "http://manu.sporny.org/"},
  "http://schema.org/image": {"@id": "http://manu.sporny.org/images/manu.png"}
};
const context = {
  "name": "http://schema.org/name",
  "homepage": {"@id": "http://schema.org/url", "@type": "@id"},
  "image": {"@id": "http://schema.org/image", "@type": "@id"}
};

compact

// compact a document according to a particular context
const compacted = await jsonld.compact(doc, context);
console.log(JSON.stringify(compacted, null, 2));
/* Output:
{
  "@context": {...},
  "name": "Manu Sporny",
  "homepage": "http://manu.sporny.org/",
  "image": "http://manu.sporny.org/images/manu.png"
}
*/

// compact using URLs
const compacted = await jsonld.compact(
  'http://example.org/doc', 'http://example.org/context', ...);

expand

// expand a document, removing its context
const expanded = await jsonld.expand(compacted);
/* Output:
{
  "http://schema.org/name": [{"@value": "Manu Sporny"}],
  "http://schema.org/url": [{"@id": "http://manu.sporny.org/"}],
  "http://schema.org/image": [{"@id": "http://manu.sporny.org/images/manu.png"}]
}
*/

// expand using URLs
const expanded = await jsonld.expand('http://example.org/doc', ...);

flatten

// flatten a document
const flattened = await jsonld.flatten(doc);
// output has all deep-level trees flattened to the top-level

frame

// frame a document
const framed = await jsonld.frame(doc, frame);
// output transformed into a particular tree structure per the given frame

canonize (normalize)

// canonize (normalize) a document using the RDF Dataset Normalization Algorithm
// (URDNA2015), see:
const canonized = await jsonld.canonize(doc, {
  algorithm: 'URDNA2015',
  format: 'application/n-quads'
});
// canonized is a string that is a canonical representation of the document
// that can be used for hashing, comparison, etc.

toRDF (N-Quads)

// serialize a document to N-Quads (RDF)
const nquads = await jsonld.toRDF(doc, {format: 'application/n-quads'});
// nquads is a string of N-Quads

fromRDF (N-Quads)

// deserialize N-Quads (RDF) to JSON-LD
const doc = await jsonld.fromRDF(nquads, {format: 'application/n-quads'});
// doc is JSON-LD

Custom RDF Parser

// register a custom synchronous RDF parser
jsonld.registerRDFParser(contentType, input => {
  // parse input to a jsonld.js RDF dataset object... and return it
  return dataset;
});

// register a custom promise-based RDF parser
jsonld.registerRDFParser(contentType, async input => {
  // parse input into a jsonld.js RDF dataset object...
  return new Promise(...);
});

Custom Document Loader

// how to override the default document loader with a custom one -- for
// example, one that uses pre-loaded contexts:

// define a mapping of context URL => context doc
const CONTEXTS = {
  "http://example.com": {
    "@context": ...
  }, ...
};

// grab the built-in Node.js doc loader
const nodeDocumentLoader = jsonld.documentLoaders.node();
// or grab the XHR one: jsonld.documentLoaders.xhr()

// change the default document loader
const customLoader = async (url, options) => {
  if(url in CONTEXTS) {
    return {
      contextUrl: null, // this is for a context via a link header
      document: CONTEXTS[url], // this is the actual document that was loaded
      documentUrl: url // this is the actual context URL after redirects
    };
  }
  // call the default documentLoader
  return nodeDocumentLoader(url);
};
jsonld.documentLoader = customLoader;

// alternatively, pass the custom loader for just a specific call:
const compacted = await jsonld.compact(
  doc, context, {documentLoader: customLoader});

Node.js Document Loader User-Agent

It is recommended to set a default user-agent header for Node.js applications. The default for the default Node.js document loader is jsonld.js.

Events

WARNING: This feature is experimental and the API, events, codes, levels, and messages may change.

Various events may occur during processing. The event handler system allows callers to handle events as appropriate. Use cases can be as simple as logging warnings, to displaying helpful UI hints, to failing on specific conditions.

Note: By default no event handler is used. This is due to general performance considerations and the impossibility of providing a default handler that would work for all use cases. Event construction and the handling system are avoided by default providing the best performance for use cases where data quality is known events are unnecessary.

Event Structure

Events are JSON objects with the following properties:

  • type: ['JsonLdEvent'] and optionally an array with others.
  • code: A basic string code, similar to existing JSON-LD error codes.
  • level: The severity level. Currently only warning is emitted.
  • message: A human readable message describing the event.
  • details: A JSON object with event specific details.

Event Handlers

Event handlers are chainable functions, arrays of handlers, objects mapping codes to handlers, or any mix of these structures. Each function is passed an object with two properties:

  • event: The event data.
  • next: A function to call to an event and a next.

The event handling system will process the handler structure, calling all handlers, and continuing onto the next handler if next() is called. To stop processing, throw an error, or return without calling next().

This design allows for composable handler structures, for instance to handle some conditions with a custom handler, and default to generic "unknown event" or logging handler.

Note: Handlers are currently synchronous due to possible performance issues. This may change to an async/await design in the future.

// expand a document with a logging event handler
const expanded = await jsonld.expand(data, {
  // simple logging handler
  eventHandler: function({event, next}) {
    console.log('event', {event});
  }
});
function logEventHandler({event, next}) {
  console.log('event', {event});
  next();
}

function noWarningsEventHandler({event, next}) {
  if(event.level === 'warning') {
    throw new Error('No warnings!', {event});
  }
  next();
}

function unknownEventHandler({event, next}) {
  throw new Error('Unknown event', {event});
}

// expand a document with an array of event handlers
const expanded = await jsonld.expand(data, {
  // array of handlers
  eventHandler: [
    logEventHandler,
    noWarningsEventHandler,
    unknownEventHandler
  ]}
});
const handler = {
  'a mild event code': function({event}) {
    console.log('the thing happened', {event});
  },
  'a serious event code': function({event}) {
    throw new Error('the specific thing happened', {event});
  }
};
// expand a document with a code map event handler
const expanded = await jsonld.expand(data, {eventHandler});

Safe Validation

A common use case is to avoid JSON-LD constructs that will result in lossy behavior. The JSON-LD specifications have notes about when data is dropped. This can be especially important when calling [canonize][] in order to digitally sign data. The event system can be used to detect and avoid these situations. A special "safe mode" is available that will inject an initial event handler that fails on conditions that would result in data loss. More benign events may fall back to the passed event handler, if any.

Note: This mode is designed to be the common way that digital signing and similar applications use this library.

The safe options flag set to true enables this behavior:

// expand a document in safe mode
const expanded = await jsonld.expand(data, {safe: true});
// expand a document in safe mode, with fallback handler
const expanded = await jsonld.expand(data, {
  safe: true
  eventHandler: function({event}) { /* ... */ }
});

Available Handlers

Some predefined event handlers are available to use alone or as part of a more complex handler:

  • safeEventHandler: The handler used when safe is true.
  • logEventHandler: A debugging handler that outputs to the console.
  • logWarningHandler: A debugging handler that outputs warning level events to the console.
  • unhandledEventHandler: Throws on all events not yet handled.

Default Event Handler

A default event handler can be set. It will be the only handler when not in safe mode, and the second handler when in safe mode.

// fail on unknown events
jsonld.setDefaultEventHandler(jsonld.unhandledEventHandler);
// will use unhandled event handler by default
const expanded = await jsonld.expand(data);
// always use safe mode event handler, ignore other events
jsonld.setDefaultEventHandler(jsonld.safeEventHandler);
// will use safe mode handler, like `{safe: true}`
const expanded = await jsonld.expand(data);

Related Modules

  • jsonld-cli: A command line interface tool called jsonld that exposes most of the basic jsonld.js API.
  • jsonld-request: A module that can read data from stdin, URLs, and files and in various formats and return JSON-LD.

Commercial Support

Commercial support for this library is available upon request from Digital Bazaar: [email protected]

Source

The source code for the JavaScript implementation of the JSON-LD API is available at:

http://github.com/digitalbazaar/jsonld.js

Tests

This library includes a sample testing utility which may be used to verify that changes to the processor maintain the correct output.

The main test suites are included in external repositories. Check out each of the following:

https://github.com/w3c/json-ld-api
https://github.com/w3c/json-ld-framing
https://github.com/json-ld/json-ld.org
https://github.com/json-ld/normalization

They should be sibling directories of the jsonld.js directory or in a test-suites dir. To clone shallow copies into the test-suites dir you can use the following:

npm run fetch-test-suites

Node.js tests can be run with a simple command:

npm test

If you installed the test suites elsewhere, or wish to run other tests, use the JSONLD_TESTS environment var:

JSONLD_TESTS="/tmp/org/test-suites /tmp/norm/tests" npm test

This feature can be used to run the older json-ld.org test suite:

JSONLD_TESTS=/tmp/json-ld.org/test-suite npm test

Browser testing can be done with Karma:

npm run test-karma
npm run test-karma -- --browsers Firefox,Chrome

Code coverage of node tests can be generated in coverage/:

npm run coverage

To display a full coverage report on the console from coverage data:

npm run coverage-report

The Mocha output reporter can be changed to min, dot, list, nyan, etc:

REPORTER=dot npm test

Remote context tests are also available:

# run the context server in the background or another terminal
node tests/remote-context-server.js

JSONLD_TESTS=`pwd`/tests npm test

To generate EARL reports:

# generate the EARL report for Node.js
EARL=earl-node.jsonld npm test

# generate the EARL report for the browser
EARL=earl-firefox.jsonld npm run test-karma -- --browser Firefox

To generate an EARL report with the json-ld-api and json-ld-framing tests as used on the official JSON-LD Processor Conformance page

JSONLD_TESTS="`pwd`/../json-ld-api/tests `pwd`/../json-ld-framing/tests" EARL="jsonld-js-earl.jsonld" npm test

The EARL .jsonld output can be converted to .ttl using the [rdf][] tool:

rdf serialize jsonld-js-earl.jsonld --output-format turtle -o jsonld-js-earl.ttl

Optionally follow the report instructions to generate the HTML report for inspection. Maintainers can submit updated results as needed.

Benchmarks

Benchmarks can be created from any manifest that the test system supports. Use a command line with a test suite and a benchmark flag:

JSONLD_TESTS=/tmp/benchmark-manifest.jsonld JSONLD_BENCHMARK=1 npm test

EARL reports with benchmark data can be generated with an optional environment details:

JSONLD_TESTS=`pwd`/../json-ld.org/benchmarks/b001-manifiest.jsonld JSONLD_BENCHMARK=1 EARL=earl-test.jsonld TEST_ENV=1 npm test

See tests/test.js for more TEST_ENV control and options.

These reports can be compared with the benchmarks/compare/ tool and at the JSON-LD Benchmarks site.

About

A JSON-LD Processor and API implementation in JavaScript

json-ld.org/

Topics

javascript linked-data rdf semantic-web json-ld

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