npm package: @rdfjs/serializer-jsonld-ext
Description: JSON-LD serializer that implements the RDF/JS Sink interface and supports different output styles
Author: Thomas Bergwinkl
Latest version: 4.0.2

# @rdfjs/serializer-jsonld-ext

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JSON-LD serializer that implements the [RDF/JS Sink interface](http://rdf.js.org/stream-spec/#sink-interface) and supports different output styles.
This package handles the stream processing and uses [jsonld.js](https://github.com/digitalbazaar/jsonld.js) for the actual serialization process. 

## Usage

The package exports the serializer as a class, so an instance must be created before it can be used.
The `.import` method, as defined in the [RDF/JS specification](http://rdf.js.org/#sink-interface), must be called to do the actual serialization.
It expects a quad stream as argument.
The method will return a stream which emits the JSON-LD as a plain object or string.

The constructor accepts an `options` object with the following optional keys:

- `baseIRI`: A base IRI given as `NamedNode`, `URL`, or string object.
- `context`: JSON-LD context that will be used for compact, flatten or frame.
  The context must be given as a plain object.
  By default `{}` is used.
- `compact`: If this flag is `true`, the jsonld.js compact will be used to process the output. 
- `flatten`: If this flag is `true`, the jsonld.js flatten will be used to process the output.
- `frame`: If this flag is `true`, the jsonld.js frame will be used to process the output.
- `skipContext`: Removes the `@context` property from the output.
  Useful for HTTP server when the media type `application/json` is used and a context is provided as header link. 
- `encoding`: Defines the encoding of the output.
  Supported encodings are `string` and `object`.
  By default `object` is used.
- `prettyPrint`: Enables pretty printing for string encoding.

It's also possible to pass options as second argument to the `.import` method.
The options from the constructor and the `.import` method will be merged together.

### Example

This example shows how to create a serializer instance and how to feed it with a stream of quads.
The output will be processed with `compact` using the given context and baseIRI.
The string emitted by the serializer will be written to the console.

```javascript
import rdf from '@rdfjs/data-model'
import { Readable } from 'readable-stream'
import SerializerJsonld from '@rdfjs/serializer-jsonld-ext'

const context = {
  '@vocab': 'http://schema.org/'
}

const serializerJsonld = new SerializerJsonld({
  baseIRI: 'http://example.org/',
  context,
  compact: true,
  encoding: 'string',
  prettyPrint: true
})

const input = new Readable({
  objectMode: true,
  read: () => {
    input.push(rdf.quad(
      rdf.namedNode('http://example.org/sheldon-cooper'),
      rdf.namedNode('http://schema.org/givenName'),
      rdf.literal('Sheldon')))
    input.push(rdf.quad(
      rdf.namedNode('http://example.org/sheldon-cooper'),
      rdf.namedNode('http://schema.org/familyName'),
      rdf.literal('Cooper')))
    input.push(rdf.quad(
      rdf.namedNode('http://example.org/sheldon-cooper'),
      rdf.namedNode('http://schema.org/knows'),
      rdf.namedNode('http://example.org/amy-farrah-fowler')))
    input.push(null)
  }
})

const output = serializerJsonld.import(input)

output.on('data', jsonld => {
  console.log(jsonld)
})

/* output:

{
  "@context": {
    "@vocab": "http://schema.org/",
    "@base": "http://example.org/"
  },
  "@id": "sheldon-cooper",
  "familyName": "Cooper",
  "givenName": "Sheldon",
  "knows": {
    "@id": "amy-farrah-fowler"
  }
}
*/
```