function savePdf() {
    console.log('hi');
    var element = '';    element = document.getElementsByName('mycontents')[0];
    var opt = {
        margin: [2, 2, 2, 2],
        filename: 'myfile',
        image: { type: 'jpeg', quality: 0.7 },
        html2canvas: { scale: 2, useCORS: true },
        jsPDF: { format: 'a4', unit: 'mm' },
        //  pagebreak: { before: '.i-pdf--page' },
    };

    
    html2pdf().from(element).set(opt).toPdf().get('pdf').then(function (pdf) {

        pdf.setFontSize(10);
    }).get('pdf').then(function (pdf) {

        console.log('hi');
        var pdfBase64 = pdf.output();
        console.log(pdfBase64);
        var pdfcontent = {};

        pdfcontent.PDFBase64 = pdfBase64;
        pdfcontent.FileName = fileName;


        $.ajax({
            type: "POST",
            url: "/pdf/savepdf",
            data: "{pdfcontent:" + JSON.stringify(pdfcontent) + "}",
            contentType: "application/json;charset=utf-8",
            datatype: "json",
            complete: OnComplete
        });
    })
}

Here is complete code in c#, javascript Save a PDF generated from html2pdf in C#, MVC , html2pdf , Ajax