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

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 tabs = new docusign.Tabs();
      tabs.setSignHereTabs(signHereTabs);
      signer.setTabs(tabs);

      // add recipients (in this case a single signer) to the envelope
      envDef.setRecipients(new docusign.Recipients());
      envDef.getRecipients().setSigners([]);
      envDef.getRecipients().getSigners().push(signer);

      // set envelope's |status| to "created" so we can open the embedded sending view next
      envDef.setStatus('created');

      // use the |accountId| we retrieved through the Login API to create the Envelope
      var loginAccount = new docusign.LoginAccount();
      loginAccount = loginAccounts[0];
      var accountId = loginAccount.accountId;