angular实现页面打印局部功能的思考与方法

 this.cach.setBylocal({key: key, value: data}); // 写入缓存
 this.router.navigate([url, key]); // 路由跳转，缓存key值传递过去

 ngAfterViewInit() {
 const $qus = this.route.params.subscribe(q => {
  const key = q.key;
  if (key) {
  this._data = this.cach.getBylocal(key) ;
  this.cach.removeBylocal(key);
  setTimeout(() => {
   window.print();
   history.go(-1);
  }, '20');
  }
 });
 }

 private down(url: string, body?: any) {
 return this.http.post(url, body || null, {
  responseType: 'blob'
 })
 }
 private downLoad(url: string, type: string, body?: any, fileName?: string) {
 return this.down(url, body).map(r => {
  const blob = new Blob([r], {type: type});
  const objectUrl = URL.createObjectURL(blob);
  const a = document.createElement('a');
  document.body.appendChild(a);
  a.setAttribute('style', 'display:none');
  a.setAttribute('href', objectUrl);
  if (fileName) {
  a.setAttribute('download', fileName);
  } else {
  a.setAttribute('target', '_blank');
  }
  a.click();
  URL.revokeObjectURL(objectUrl);
  return true;
 });
 }

 /**
 * 下载pdf， 如果不传入文件名会再浏览器中打开 实现打印功能
 * 传入文件名会直接下载
 * @param {string} url
 * @param body
 * @param {string} fileName
 * @returns {Observable<boolean>}
 */
 downLoadPdf(url: string, body?: any, fileName?: string) {
 return this.downLoad(url, 'application/pdf', body, fileName);
 }