Bindings cannot contain assignments 绑定不能包含赋值

Bindings cannot contain assignments：

<tr *ngIf="options.isGroup">
  <th nzLeft="0px" rowspan="2">序号</th>
  <ng-container *ngFor="let group of options.nodes">
  <th *ngIf="getHeaderGroupLength(group.children); let l" [colspan]="l">
     {{group.label}}</th>
  </ng-container>
</tr>

getHeaderGroupLength(headers: any[]): number {
  return headers.filter(item => item.checked).length;
}