js 下载流调用浏览器预览 的方法

//文件预览js 下载流调用浏览器预览 的方法
var $viewblob=function (url, data) {
  const config = { responseType: 'blob', timeout: 9999999 };
  $http(url,data,config).then(res => {
    const fileRes =res;
    let type = { type: 'application/octet-stream' };
    const types = {
        pdf: { type: 'application/pdf' },
        png: { type: 'image/png' },
        jpg: { type: 'image/jpeg' },
    }

    let contentDisposition = res.headers["content-disposition"]||"filename=未知文件";
    let patt = new RegExp("filename=([^;]+\\.[^\\.;]+);*");
    let result = patt.exec(contentDisposition);
    const filename =  decodeURI(contentDisposition).split('=')[1].replace('\'','').replace('"','');

    if (filename) {
        const suffix = filename.substring(filename.lastIndexOf('.') + 1).toLocaleLowerCase();
        if (types[suffix]) { //预览
            type = types[suffix];
            //其他下载 octet-stream
        }
    }

    let viewurl= window.URL && window.URL.createObjectURL(new Blob([fileRes.blob], type));
    if(viewurl){
      window.open(viewurl)
    }
  })
}