title: Property 'app' does not exist on type 'AppComponent'
body: <p>I am new to angular working on a CRUD app . Aim is to download mongoDB data to Excel via angular using a download button. While building that ,I am getting this error <br>
  Error in in src/app/app.component.html:28:26 - error TS2339 Property 'app' does not exist on type 'AppComponent'.</p>
  <p><strong>code</strong> <br>
  app.component.html <br></p>
  <pre><code>&lt;div&gt;
    &lt;nav class=&quot;navbar navbar-expand navbar-dark bg-dark&quot;&gt;
      &lt;a href=&quot;#&quot; class=&quot;navbar-brand&quot;&gt;HOME&lt;/a&gt; #bezKoder
      &lt;div class=&quot;navbar-nav mr-auto&quot;&gt;
        &lt;li class=&quot;nav-item&quot;&gt;
          &lt;a routerLink=&quot;tutorials&quot; class=&quot;nav-link&quot;&gt;Tutorials&lt;/a&gt;
        &lt;/li&gt;
        &lt;li class=&quot;nav-item&quot;&gt;
          &lt;a routerLink=&quot;add&quot; class=&quot;nav-link&quot;&gt;Add&lt;/a&gt;
        &lt;/li&gt;
      &lt;/div&gt;
      
      &lt;a style=&quot;cursor: pointer&quot; (click)=&quot;exportexcel()&quot;&gt;
        
      &lt;/a&gt;
    &lt;/nav&gt;
  
    &lt;div class=&quot;container mt-3&quot;&gt;
      &lt;router-outlet&gt;&lt;/router-outlet&gt;
    &lt;/div&gt;
  &lt;/div&gt;&gt;
  &lt;table id=&quot;excel-table&quot;&gt; 
    &lt;tr&gt;       
       &lt;th&gt;title&lt;/th&gt; 
       &lt;th&gt;description&lt;/th&gt;  
          
    &lt;/tr&gt;    
    &lt;tr *ngFor=&quot;let sup of app&quot;&gt;
    // This is the binding part. 
       &lt;td&gt;{{ sup.title }}&lt;/td&gt;  
       &lt;td&gt;{{ sup.description }}&lt;/td&gt; 
  
    &lt;/tr&gt; 
  </code></pre>
  
  <br>
  app.component.ts <br>
  <pre><code>import { Component } from '@angular/core';
  import * as XLSX from 'xlsx'; 
  
  
  @Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
  })
  export class AppComponent {
    title = 'Angular10Crud';
    /*name of the excel-file which will be downloaded. */ 
  fileName= 'tutorials_data.xlsx';  
  
  exportexcel(): void 
      {
         /* table id is passed over here */   
         let element = document.getElementById('excel-table'); 
         const ws: XLSX.WorkSheet =XLSX.utils.table_to_sheet(element);
  
         /* generate workbook and add the worksheet */
         const wb: XLSX.WorkBook = XLSX.utils.book_new();
         XLSX.utils.book_append_sheet(wb, ws, 'Sheet1');
  
         /* save to file */
         XLSX.writeFile(wb, this.fileName);
    
      }
  }
  </code></pre>