title: JSPDF .html() function returning blank pdf page
body: <p>Using the new jsPDF .html() pretty much pulled straight from their docs, but it still results in a blank page:</p>
  
  <p>Results in blank page:</p>
  
  <pre><code>function saveDoc() {
    window.html2canvas = html2canvas
    const doc = document.getElementById('doc')
  
    if (doc) {
  
          var pdf = new jsPDF('p', 'pt', 'a4')
          pdf.html(doc.innerHTML, {
             callback: function (pdf) {
               pdf.save('DOC.pdf');
             }
          })
    }
  }
  </code></pre>
  
  <p>Results in no PDF generated:</p>
  
  <pre><code>function saveDoc() {
    window.html2canvas = html2canvas
    const doc = document.getElementById('doc')
  
    if (doc) {
  
          var pdf = new jsPDF('p', 'pt', 'a4')
          pdf.html(doc.innerHTML, {
             function (pdf) {
               pdf.save('DOC.pdf');
             }
          })
    }
  }
  </code></pre>
  
  <p>Also results in blank page:</p>
  
  <pre><code>function saveDoc() {
    window.html2canvas = html2canvas
    const doc = document.getElementById('doc')
  
    if (doc) {
  
          var pdf = new jsPDF('p', 'pt', 'a4')
          pdf.html(doc, {
             callback: function (pdf) {
               pdf.save('DOC.pdf');
             }
          })
    }
  }
  </code></pre>
  
  <p>Will use another tool if there are any other suggestions. Need it to be secure and generate selectable text PDF to keep overall size down. It's a long document it's generating and when doing it via addImage() the resulting file is huge. Thoughts?</p>