How to use the jsonld.registerRDFParser function in jsonld

/// 
// tslint:disable:no-var-requires
const jsonldRdfaParser = require("jsonld-rdfa-parser");
const jsonldLib = require("jsonld");
// tslint:enable:no-var-requires
jsonldLib.registerRDFParser("text/html", jsonldRdfaParser);
import * as assert from "assert";
import * as fs from "fs";
import { ClientRequestArgs } from "http";
import * as http from "http";
import * as https from "https";
import * as path from "path";
import * as url from "url";
import { Url, UrlObject } from "url";
import * as util from "util";
import { ASLink, HttpRequestResponder } from "./types";

import { createLogger } from "../src/logger";
const logger = createLogger("util");

/**
 * Return the 'first' item of the provided itemOrList.

/**
 * convert schema.org raw RDFa data into compacted JSON-LD
 */

var fs = require('fs');
var path = require('path');
var jsonldRdfaParser = require('jsonld-rdfa-parser');
var jsonld = require('jsonld');
var request = require('request');

// register the parser for content type text/html
jsonld.registerRDFParser('text/html', jsonldRdfaParser);

var context = {
  '@context': {
    rdf: 'http://www.w3.org/1999/02/22-rdf-syntax-ns#',
    rdfs: 'http://www.w3.org/2000/01/rdf-schema#',
    owl: 'http://www.w3.org/2002/07/owl#',
    vs: 'http://www.w3.org/2003/06/sw-vocab-status/ns#',
    xsd: 'http://www.w3.org/2001/XMLSchema#',
    bibo: 'http://purl.org/ontology/bibo/',
    skos: 'http://www.w3.org/2004/02/skos/core#',
    dc: 'http://purl.org/dc/terms/',
    schema: 'http://schema.org/',
    oa: 'http://www.w3.org/ns/oa#',

    sameAs: {
      '@id': 'owl:sameAs',