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// First, you have to include jsPDF library, and also html2canvas or rasterizeHTML.
// Then, just create a jsPDF object and save to pdf the entire 'body' tag (or whatever):
var pdf = new jsPDF('p','pt','a4');
pdf.addHTML(document.body,function() {
pdf.save('web.pdf');
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/0.4.1/html2canvas.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jspdf/1.0.272/jspdf.debug.js"></script>
<body>
<p id="to-pdf">HTML content</p>
</body>