pdf.js side-by-side example

Demonstrates a simplistic side-by-side pdf viewer

by Yetangitu

HTML

<script src="//mozilla.github.io/pdf.js/build/pdf.js"></script>

<h1>PDF.js side-by-side example</h1>
<div>
  <button id="prev">Previous</button>
  <button id="next">Next</button>
  &nbsp; &nbsp;
  <span>Page: <span id="page_num"></span> / <span id="page_count"></span></span>
</div>

<div>
  <canvas id="left" class="left"></canvas>
  <canvas id="right" class="right"></canvas>
  <span id="pleft" class="left"></span>
  <span id="pright" class="right"></span>
</div>

CSS

span.left,
span.right {
  padding: 1em;
  font-size: 1.5em;
  font-weight: 600;
}

.left {
  float: left;
  clear: left;
}

.right {
  float: right;
  clear: right;
}

JavaScript

// If absolute URL from the remote server is provided, configure the CORS
// header on that server.
var url = '//cdn.mozilla.net/pdfjs/tracemonkey.pdf';

// The workerSrc property shall be specified.
PDFJS.workerSrc = '//mozilla.github.io/pdf.js/build/pdf.worker.js';

var pdfDoc = null,
  pageNum = 1,
  pageRendering = false,
  pageNumPending = null,
  scale = 1,
  canvaslst = [],
  context = [];

canvaslst.push(document.getElementById('right'));
context.push(canvaslst[0].getContext('2d'));
canvaslst.push(document.getElementById('left'));
context.push(canvaslst[1].getContext('2d'));

/**
 * Get page info from document, resize canvas accordingly, and render page.
 * @param num Page number.
 */
function renderPage(num) {
  var index = num % 2;
  var canvas = canvaslst[index];
  var ctx = context[index];
  pageRendering = true;
  // Using promise to fetch the page
  pdfDoc.getPage(num).then(function(page) {
    var viewport = page.getViewport(scale);
    canvas.height = viewport.height;
    canvas.width = viewport.width;

    // Render PDF page into canvas context
    var renderContext = {
      canvasContext: ctx,
      viewport: viewport
    };
    var renderTask = page.render(renderContext);

    // Wait for rendering to finish
    renderTask.promise.then(function() {
      pageRendering = false;
      if (pageNumPending !== null) {
        // New page rendering is pending
        renderPage(pageNumPending);
        pageNumPending = null;
      }
    });
  });

  // Update page counters
  document.getElementById('page_num').textContent = pageNum;
  document.getElementById('pleft').textContent = pageNum;
  document.getElementById('pright').textContent = pageNum + 1;
}

/**
 * If another page rendering in progress, waits until the rendering is
 * finised. Otherwise, executes rendering immediately.
 */
function queueRenderPage(num) {
  if (pageRendering) {
    pageNumPending = num;
  } else {
    renderPage(num);
    renderPage(num + 1)
  }
}

/**
 * Displays...