@rdfjs/fetch

@rdfjs/fetch

Wrapper for fetch to simplify sending and retrieving RDF data.

Since version 3.0, this packages is ESM only. Check version 2.x if you are looking for a CommonJS package.

Usage

The package exports a fetch function which wraps the request and response object for on-the-fly RDF quad processing. The function accepts the same parameters as fetch and some additional options. It also provides extra methods.

Options

The options object accepts the following additional parameters:

• formats: A formats-common-compatible object which contains a set of parsers and serializers. By default formats-common is used.
• factory: The factory which will be used to create a Dataset when dataset() is called. By default @rdfjs/dataset is used.
• fetch: An alternative fetch implementation. By default nodeify-fetch is used.

The following options influence the logic of RDF quad processing:

• headers.accept: The accept header field will be automatically set base on the list of available parsers from the formats object. If it's already set it will not be overwritten. This can be useful when only a subset of the available parsers should be used.
• headers.content-type: When the request has a body, this header field will be automatically set to use matching media type for the corresponding serializer. By setting this field manually a specific serializer can be enforced.
• body: If the request should send quads, the quads must be given either as a stream or as an iterable like a DatasetCore object. Iterables will be converted to streams before they are handed over to the serializer.

Response

The following methods are attached to the standard fetch response object:

• async quadStream(): This method returns the quads of the response as stream. The parser is selected based on the content type header field.
• async dataset(): This method uses the quadStream() method to parse the content and will pipe it into a dataset, which is also the return value.

Example

This example fetches the RDF Schema vocab and loops over all quad using the dataset API. For all rdfs:label quads the object value is written to the console.

const fetch = require('@rdfjs/fetch')

const label = 'http://www.w3.org/2000/01/rdf-schema#label'

fetch('http://www.w3.org/2000/01/rdf-schema')
  .then(res => res.dataset())
  .then(dataset => {
    for (const quad of dataset) {
      if (quad.predicate.value === label) {
        console.log(`${quad.subject.value}: ${quad.object.value}`)
      }
    }
  })
  .catch(err => console.error(err))