title: Can't save pptx with image in blob format - pptxGenJS
body: <p>I want to create a pptx file with javascript and send it to the server. 
  To do so, I am going to create a pptx file as blob.</p>
  
  <p>Generating from the regular Client Browser, not Node.js. Below is the pptxGenjs site.
  <a href="https://gitbrent.githubio/PptxGenJS/docs/usage-save.html" rel="nofollow noreferrer">https://gitbrent.githubio/PptxGenJS/docs/usage-save.html</a></p>
  
  <p>The problem is not created as blob when pptx containing the image.
  When I print out a log on the console, only the name of pptx is shown.
  (It shall be printed on the console in the form of a blob.)</p>
  
  <pre><code>        ...
          var ppt_name = 'AAAA.pptx';
  
          var pptx = new PptxGenJS();
          pptx.setLayout('LAYOUT_4x3');
          pptx.defineSlideMaster({          
              title: 'MASTER_SLIDE',
              bkgd: 'FFFFFF',
              objects: [
                  { 'text':  { text:'Writer', options:{ x:6.5, y:0.2, fontSize:8 } } },
                  { 'text':  { text:'Date', options:{ x:8.0, y:0.2, fontSize:8 } } }
              ],
              slideNumber: {x: 0.3, y: '90%'}});
          var slide = pptx.addNewSlide('MASTER_SLIDE');
  
          slide.addImage({x: 0.5, y: 2.40, w: 2.67, h: 2.0, path:"/assets/main/AAA/AAA.png"});
  
          pptx.save(ppt_name, function(blob){console.log(blob);},'blob');
          ...
  </code></pre>
  
  <p>But when I changed last part of the same code, (Download .pptx by download prompt) image is well included in pptx.
   pptx.save(ppt_name);</p>
  
  <p>and here is my console output.</p>
  
  <p><a href="https://i.stack.imgur.com/K76w2.png" rel="nofollow noreferrer">When using slide.addimage</a></p>
  
  <p><a href="https://i.stack.imgur.com/0UUWD.png" rel="nofollow noreferrer">When slide.addimage is not used</a></p>
  
  <p>What is the cause?
  Thanks!</p>