折腾半天，找到两种。

1.通过html2canvas和jspdf生成pdf

因为通过canvas做中介，所以缺点是很慢。

   const htmlString=`
   <div>
        <div>
            123
        </div>
    </div>
   `;
   const parser = new DOMParser();
   const htmlDoc = parser.parseFromString(htmlString, 'text/html');
   const iframe= document.createElement("iframe");
   document.body.appendChild(iframe); 
   iframe.contentWindow.document.open();
   iframe.contentWindow.document.write(htmlDoc.body.outerHTML);
   iframe.contentWindow.document.close();
   html2canvas(iframe.contentWindow.document.body).then(function(canvas) {
     const pdf = new jsPDF(undefined, 'pt', 'a4');
     pdf.addImage(canvas.toDataURL('image/jpeg'), 'JPEG', 0, 0, pdf.internal.pageSize.width, canvas.height * pdf.internal.pageSize.width / canvas.width);
     pdf.save('example.pdf');
     document.body.removeChild(iframe)
   });

2.通过浏览器的print方法

推荐用这种方式。

   function htmlToPdf(htmlString) {
    var iframe = document.createElement('iframe');
    iframe.style.display = 'none';
    document.body.appendChild(iframe);
    var doc = iframe.contentWindow.document;
    doc.body.innerHTML=htmlString
    var win = iframe.contentWindow;
    win.print();
    document.body.removeChild(iframe)
   }
   const htmlString=`
   <div>
        <div>
            123
        </div>
    </div>
   `;
   const parser = new DOMParser();
   const htmlDoc = parser.parseFromString(htmlString, 'text/html');
   const htmlString=htmlDoc.body.innerHTML
   htmlToPdf(htmlString)