Angular2 判断上传的.txt文件内容是不是对象 如果上传文件列表有一个了 则替代之前的文件 如果上传文件不是.txt文件 则清空上传文件列表

     if(this.documentUpload.substr(0,1) == '{' && this.documentUpload.substr(-1,1) == '}'){}
 
　　　if(this.fileList.length > 1){
       this.fileList = this.fileList.slice(-1);
     }
　　　this.fileList = [];
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const filterFiles = fileLists.filter(w => ~['text/plain'].indexOf(w.type));
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  filterPic: UploadFilter[] = [           //过滤器  上传列表数量的限制
    {
      name: 'type',
      fn: (fileListPic: UploadFile[]) => {
        // var filetypes =[".jpg",".png",".rar",".txt",".zip",".doc",".ppt",".xls",".pdf",".docx",".xlsx"];
        const filterFiles = fileListPic.filter(w => ~['image/png','image/jpeg','image/gif','image/bmp'].indexOf(w.type));
        // const filterFiles = fileLists.filter(w => ~["/txt","/doc"].indexOf(w.type));
        if (filterFiles.length !== fileListPic.length) {
          this.msg.error(`包含文件格式不正确，只支持image/png,image/jpeg,image/gif,image/bmp格式`);
          return filterFiles;
        }
        return fileListPic;
      }
    },
    {
      name: 'async',
      fn: (fileListsPic: UploadFile[]) => {
        return new Observable((observer: Observer<UploadFile[]>) => {
          // doing
          observer.next(fileListsPic);
          observer.complete();
        });
      }
    }
  ];
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  <div nz-row class="serveKey">
    <div nz-col nzSpan="1"></div>
    <div nz-col nzSpan="18">
      <nz-upload
        [nzFileType]="'image/png,image/jpeg,image/gif,image/bmp'"
        [nzAction]="url + '/publish/upload/pic'"
        [nzFileList]="fileListPic"
        [nzFilter]="filterPic"
        nzMultiple
        [nzLimit]="2"
        (nzChange)="picChange($event)"
      >
        <button nz-button style="margin: 0;"><i nz-icon nzType="upload"></i><span>图片上传</span></button>
      </nz-upload>
      <span *ngIf="ngText&&publish.imagePath == ''" style="margin-top:5px;display: block;color: #f5707a;">不能为空</span>

    </div>
    <div nz-col nzSpan="1">
      <div *ngIf="publish.imagePath !== ''" style="display:inline-block;vertical-align:middle;margin-left: 6px;">
        <i nz-icon  [nzType]="'check-circle'" [nzTheme]="'twotone'" [nzTwotoneColor]="'#52c41a'"></i>
      </div>
    </div>
  </div>