// .html file
<app-tinymce class="note-input-textarea" [(ngModel)]='noteText'
          [ngClass]="{
                       strikethrough: isDeleted
                     }"
          [disabled]="canUpdateNoteDetail">
    </app-tinymce>

// .scss file
.strikethrough {
  text-decoration: line-through;
}

// .ts file
 export class UpdateProgressNotePage {
  @ViewChild(TinymceComponent) private tinyMce: TinymceComponent;
  isDeleted: boolean = true;
   constructor(){
     this.initialize();
   }

   initialize() {
     if(isDeleted) {
       this.tinyMce.editor.execCommand('Strikethrough', false);
     }
   }

 }