How to use the jsonld.clone function in jsonld

async function _generateCredential() {
  const mockCredential = jsonld.clone(mockData.credentials.alpha);
  const {authenticationKey, documentLoader} = await _generateDid();
  const {Ed25519Signature2018} = jsigs.suites;
  const {AuthenticationProofPurpose} = jsigs.purposes;
  testLoader.addLoader(documentLoader);
  const credential = await jsigs.sign(mockCredential, {
    compactProof: false,
    documentLoader: testLoader.documentLoader.bind(testLoader),
    suite: new Ed25519Signature2018({key: authenticationKey}),
    purpose: new AuthenticationProofPurpose({
      challenge: 'challengeString'
    })
  });
  return {credential, documentLoader};
}

async function _generatePresentation({challenge, domain}) {
  const mockPresentation = jsonld.clone(mockData.presentations.alpha);
  const {authenticationKey, documentLoader: dlp} = await _generateDid();
  testLoader.addLoader(dlp);
  const {Ed25519Signature2018} = jsigs.suites;
  const {AuthenticationProofPurpose} = jsigs.purposes;
  const {credential, documentLoader: dlc} = await _generateCredential();
  testLoader.addLoader(dlc);
  mockPresentation.verifiableCredential.push(credential);
  const presentation = await jsigs.sign(mockPresentation, {
    compactProof: false,
    documentLoader: testLoader.documentLoader.bind(testLoader),
    suite: new Ed25519Signature2018({key: authenticationKey}),
    purpose: new AuthenticationProofPurpose({challenge, domain})
  });
  return {presentation};
}