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@rdfjs/fetch-lite
Wrapper for fetch to simplify sending and retrieving RDF data.
This is a light version of the @rdfjs/fetch
package, without the @rdfjs/formats-common
dependency.
It is useful when you want to make a build for the browser with a reduced set of parsers and serializers.
The formats
options is required for this package.
See also the @rdfjs/fetch
documentation.
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. This parameter is required.factory
: If given, the factory will be used to create a Dataset whendataset()
is called. If the parameter is not given, thedataset()
method will not be attached to the response.fetch
: An alternative fetch implementation. By default nodeify-fetch will be 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 theformats
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. Iterables will be converted to streams before they are handed over to the serializer.prefixes
: A map of prefixes that will be 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 thequadStream()
method to parse the content and will pipe it into a dataset, which is also the return value. This method is only available when thefactory
option is given.
The Content-Type
header of the response can be changed or set before calling quadStream()
or dataset()
.
That allows enforcing a specific parser or can be used to fix a lacking header.
Example
This example fetches data from a resource on Wikidata.
The stream API is used to process all quads.
For all rdfs:label
quads of the defined entity, the object language and value will be written to the console.
import formats from '@rdfjs/formats-common'
import fetch from '@rdfjs/fetch-lite'
const entity = 'http://www.wikidata.org/entity/Q2'
const label = 'http://www.w3.org/2000/01/rdf-schema#label'
const res = await fetch('https://www.wikidata.org/wiki/Special:EntityData/Q2.ttl', { formats })
const quadStream = await res.quadStream()
quadStream.on('error', err => console.error(err))
quadStream.on('data', quad => {
if (quad.subject.value === entity && quad.predicate.value === label) {
console.log(`${quad.object.language}: ${quad.object.value}`)
}
})