无法分配对象'＃<object>'的只读属性

Question

urldata:any = {};

   constructor(private searchservice: SearchService, private route: Router, private activatedroute: ActivatedRoute,
              private store: Store<fromRoot.State>, private ref: ChangeDetectorRef, public themeService: ThemeService) {
this.activatedroute.queryParams.subscribe(query => {

  if (query['fq']) {

    if (query['fq'].includes('png')) {
      this.resultDisplay = 'images';
      this.urldata.fq = 'url_file_ext_s:(png+OR+jpeg+OR+jpg+OR+gif)';
    } else if (query['fq'].includes('avi')) {
      this.resultDisplay = 'videos';
    } else {
      this.resultDisplay = 'all';
    }
  } else {
    this.resultDisplay = 'all';
  }
  if (query['resultDisplay']) {
    this.resultDisplay = query['resultDisplay'];
    this.urldata.resultDisplay = this.resultDisplay;
  }
  this.urldata.start = query['start'] || 0 ;
  this.urldata.query = query['query'];
  this.urldata.sort = query['sort'];
  this.urldata.rows = Number(query['rows']) || 10;

  this.message = '';

  this.store.dispatch(new queryactions.QueryAction(query['query']));
  this.store.dispatch(new queryactions.QueryServerAction(this.urldata));

上面的代码给了我：

  

未捕获（承诺）：TypeError：无法分配对象'＃'错误的只读属性'start'。

什么会导致此错误？

我已在我的组件中定义了urldata: any = {}。