jsonld

jsonld.js

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.

Installation

node.js + npm

npm install jsonld

var jsonld = require('jsonld');

Browser (AMD) + npm

npm install jsonld

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

Browser + script tag

<!-- For legacy browsers include a Promise polyfill like
  es6-promise before including jsonld.js -->
<script src="//cdn.jsdelivr.net/g/es6-promise@1.0.0"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jsonld/0.5.0/jsonld.min.js"></script>

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

JSPM

jspm install npm:jsonld

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

Examples

var 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"}
};
var context = {
  "name": "http://schema.org/name",
  "homepage": {"@id": "http://schema.org/url", "@type": "@id"},
  "image": {"@id": "http://schema.org/image", "@type": "@id"}
};

// compact a document according to a particular context
// see: http://json-ld.org/spec/latest/json-ld/#compacted-document-form
jsonld.compact(doc, context, function(err, compacted) {
  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
jsonld.compact('http://example.org/doc', 'http://example.org/context', ...);

// expand a document, removing its context
// see: http://json-ld.org/spec/latest/json-ld/#expanded-document-form
jsonld.expand(compacted, function(err, expanded) {
  /* 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
jsonld.expand('http://example.org/doc', ...);

// flatten a document
// see: http://json-ld.org/spec/latest/json-ld/#flattened-document-form
jsonld.flatten(doc, function(err, flattened) {
  // all deep-level trees flattened to the top-level
});

// frame a document
// see: http://json-ld.org/spec/latest/json-ld-framing/#introduction
jsonld.frame(doc, frame, function(err, framed) {
  // document transformed into a particular tree structure per the given frame
});

// normalize a document using the RDF Dataset Normalization Algorithm
// (URDNA2015), see: http://json-ld.github.io/normalization/spec/
jsonld.normalize(doc, {
  algorithm: 'URDNA2015',
  format: 'application/nquads'
}, function(err, normalized) {
  // normalized is a string that is a canonical representation of the document
  // that can be used for hashing, comparison, etc.
});

// serialize a document to N-Quads (RDF)
jsonld.toRDF(doc, {format: 'application/nquads'}, function(err, nquads) {
  // nquads is a string of nquads
});

// deserialize N-Quads (RDF) to JSON-LD
jsonld.fromRDF(nquads, {format: 'application/nquads'}, function(err, doc) {
  // doc is JSON-LD
});

// register a custom async-callback-based RDF parser
jsonld.registerRDFParser = function(contentType, function(input, callback) {
  // parse input to a jsonld.js RDF dataset object...
  callback(err, dataset);
});

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

// use the promises API
var promises = jsonld.promises;

// compaction
var promise = promises.compact(doc, context);
promise.then(function(compacted) {...}, function(err) {...});

// expansion
var promise = promises.expand(doc);
promise.then(function(expanded) {...}, function(err) {...});

// flattening
var promise = promises.flatten(doc);
promise.then(function(flattened) {...}, function(err) {...});

// framing
var promise = promises.frame(doc, frame);
promise.then(function(framed) {...}, function(err) {...});

// normalization
var promise = promises.normalize(doc, {format: 'application/nquads'});
promise.then(function(normalized) {...}, function(err) {...});

// serialize to RDF
var promise = promises.toRDF(doc, {format: 'application/nquads'});
promise.then(function(nquads) {...}, function(err) {...});

// deserialize from RDF
var promise = promises.fromRDF(nquads, {format: 'application/nquads'});
promise.then(function(doc) {...}, function(err) {...});

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

// 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
var CONTEXTS = {
  "http://example.com": {
    "@context": ...
  }, ...
};

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

// change the default document loader using the callback API
// (you can also do this using the promise-based API, return a promise instead
// of using a callback)
var customLoader = function(url, callback) {
  if(url in CONTEXTS) {
    return callback(
      null, {
        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 underlining documentLoader using the callback API.
  nodeDocumentLoader(url, callback);
  /* Note: By default, the node.js document loader uses a callback, but
  browser-based document loaders (xhr or jquery) return promises if they
  are supported (or polyfilled) in the browser. This behavior can be
  controlled with the 'usePromise' option when constructing the document
  loader. For example: jsonld.documentLoaders.xhr({usePromise: false}); */
};
jsonld.documentLoader = customLoader;

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

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: [e-mail]

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/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

Browser testing can be done with Karma:

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

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

npm run coverage

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=./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 test-karma -- --browser Firefox

Changelog

0.5.10 - 2017-09-21

Added

• Add expansionMap and compactionMap options. These functions may be provided that will be called when an unmapped value or property will be dropped during expansion or compaction, respectively. The function map return either undefined to cause the default behavior, some other value to use instead of the default expanded/compacted value, or it may throw an error to stop expansion/compaction.

Removed

• BREAKING: Remove deprecated objectify and prependBase APIs. Now objectify can be achieved via the @link option in framing and prependBase can be found via url.prependBase.
• BREAKING: Remove deprecated namer option from all public APIs, use issuer instead.
• BREAKING: Last active context used is no longer returned as an optional parameter to the compact callback.
• BREAKING: Do not expose deprecated DocumentCache.

Changed

• BREAKING: Change default canonicalization algorithm to URDNA2015.