Angular ngFor trackBy

app.component.html

<table>
  <thead>
      <tr>
          <th>Customer ID</th>
          <th>Name</th>
          <th>Address</th>
          <th>Phone</th>
          <th>Email</th>
          <th>Gender</th>
          <th>Is First</th>
          <th>Is Last</th>
      </tr>
  </thead>
  <tbody>
      <tr *ngFor='let cust of customers; let isFirst = first; let isLast = last'>
          <td>{{cust.cust_code}}</td>
          <td>{{cust.cust_name}}</td>
          <td>{{cust.Cust_address}}</td>
          <td>{{cust.Cust_phone}}</td>
          <td>{{cust.Cust_email}}</td>
          <td>{{cust.Cust_gender}}</td>
          <td>{{isFirst}}</td>
          <td>{{isLast}}</td>
      </tr>
      <tr *ngIf="!customers || customers.length==0">
          <td colspan="7">
              No Customer to display
          </td>
      </tr>
  </tbody>
</table>