How to use the docusign-esign.Signer function in docusign-esign

var envDef = new docusign.EnvelopeDefinition();
      envDef.setEmailSubject('Please sign this document sent from Node SDK)');

      // add a document to the envelope
      var doc = new docusign.Document();
      var base64Doc = Buffer.from(fileBytes).toString('base64');
      doc.setDocumentBase64(base64Doc);
      doc.setName('TestFile.pdf'); // can be different from actual file name
      doc.setDocumentId('1');

      var docs = [];
      docs.push(doc);
      envDef.setDocuments(docs);

      // add a recipient to sign the document, identified by name and email we used above
      var signer = new docusign.Signer();
      signer.setEmail(signerEmail);
      signer.setName(signerName);
      signer.setRecipientId('1');

      // create a signHere tab somewhere on the document for the signer to sign
      // default unit of measurement is pixels, can be mms, cms, inches also
      var signHere = new docusign.SignHere();
      signHere.setDocumentId('1');
      signHere.setPageNumber('1');
      signHere.setRecipientId('1');
      signHere.setXPosition('100');
      signHere.setYPosition('100');

      // can have multiple tabs, so need to add to envelope as a single element list
      var signHereTabs = [];
      signHereTabs.push(signHere);

var envDef = new docusign.EnvelopeDefinition();
      envDef.setEmailSubject('Please sign this document sent from Node SDK)');

      // add a document to the envelope
      var doc = new docusign.Document();
      var base64Doc = Buffer.from(fileBytes).toString('base64');
      doc.setDocumentBase64(base64Doc);
      doc.setName('TestFile.pdf'); // can be different from actual file name
      doc.setDocumentId('1');

      var docs = [];
      docs.push(doc);
      envDef.setDocuments(docs);

      // add a recipient to sign the document, identified by name and email we used above
      var signer = new docusign.Signer();
      signer.setEmail(signerEmail);
      signer.setName(signerName);
      signer.setRecipientId('1');

      // Must set |clientUserId| for embedded recipients and provide the same value when requesting
      // the recipient view URL in the next step
      signer.setClientUserId('1001');

      // create a signHere tab somewhere on the document for the signer to sign
      // default unit of measurement is pixels, can be mms, cms, inches also
      var signHere = new docusign.SignHere();
      signHere.setDocumentId('1');
      signHere.setPageNumber('1');
      signHere.setRecipientId('1');
      signHere.setXPosition('100');
      signHere.setYPosition('100');