我用jsPdf（jsfiddle）做错了什么

Question

在jspdf examples page之后，我尝试在jsfiddle中重现 addHTML 演示，但iframe-pdf保持为空。检查它会显示一个空的iframe，就像在jspdf演示页面中iframe填充嵌入对象一样。

jsfiddle in question

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var pdf = new jsPDF('p', 'pt', 'a4');

pdf.addHTML($('#content')[0], function () {
    var string = pdf.output('datauristring');
    $('#preview-pane').attr('src', string);
});

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<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://html2canvas.hertzen.com/build/html2canvas.js"></script>
<script src="https://cdn.rawgit.com/MrRio/jsPDF/master/dist/jspdf.debug.js"></script>
<div id="content">
    	<h2>Have a play.</h2>

    <p>A HTML5 client-side solution for generating PDFs. Perfect for event tickets, reports, certificates, you name it!</p>
    <p><b>No servers were used in the making of this demo.</b>
    </p>
</div>
<iframe id="preview-pane" type="application/pdf" width="100%" height="300" src=""></iframe>

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我在这里缺少什么？