title: Angular: Insert new array of FormGroup inside FormArray
body: <p>Below is my code.</p>
  
  <pre><code>getAccountAssociatedDetails(account, index) {
          if (!!account) {
              this.agreementDetailsService.getDetails(account)
                  .subscribe((response) =&gt; {
                      console.log(response);
                      const rows = &lt;FormArray&gt;this.manualDetailsForm.get('rows');
                      let associatedDetailsArray = &lt;Array&lt;any&gt;&gt;response.associatedDetails;
                      let newItems = [];
                      for (let i = 0; i &lt; associatedDetailsArray.length; i++)
                          newItems.push(this.buildDetail(associatedDetailsArray[i].account, associatedDetailsArray[i].huid, associatedDetailsArray[i].huidName, associatedDetailsArray[i].huidCountry));
                      rows.splice(index, 0, ...newItems);
                  });
          }
      }
  </code></pre>
  
  <p>How to insert new array at a specific position of <code>FormArray</code>. </p>
  
  <p>I'm getting error property <code>splice</code> does not exist on type <code>FormArray</code>. Please help me some other way to do this.</p>