验证日期交叉

this.startDList = [];
   // tslint:disable-next-line:forin
   for (const a in this.vatList) {
     this.startDList.push(this.vatList[a].dateValidFrom);
   }
   this.endDList = [];
   // tslint:disable-next-line:forin
   for (const a in this.vatList) {
     this.endDList.push(this.vatList[a].dateValidTo);
   }
   const startDListSort = [...this.startDList].sort();
   const endDListSort = [...this.endDList].sort();
   for (let k = 1; k < startDListSort.length; k++) {
     if (startDListSort[k] <= endDListSort[k - 1]) {
      alert（'日期有交叉'）
     }
   }