pdf.js ludicrous example

Demonstrates a simplistic 10-page-spread pdf viewer

by Yetangitu

HTML

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

<h1>PDF.js ludicrous 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 class="page_container">
  <canvas id="c0"></canvas>
  <canvas id="c1"></canvas>
  <canvas id="c2"></canvas>
  <canvas id="c3"></canvas>
</div>
<div class="page_container">
  <canvas id="c4"></canvas>
  <canvas id="c5"></canvas>
</div>
<div class="page_container">
  <canvas id="c6"></canvas>
  <canvas id="c7"></canvas>
  <canvas id="c8"></canvas>
  <canvas id="c9"></canvas>
</div>

CSS

.page_container {
  display: flex;
  justify-content: center;
}

canvas {
  padding: 1em 0;
}

.page_container canvas:nth-of-type(odd) {
  margin-left: 1em;
  margin-right: 0;
}

.page_container canvas:nth-of-type(even) {
  margin-right: 1em;
  margin-left: 0;
}

.page_container canvas:nth-of-type(3) {
  padding-left: 1em;
}

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 = 0.4,
  canvaslst = [],
  context = [];
  
  for (var i=0; i < 10; i++) {
  	canvaslst.push(document.getElementById('c' + i));
    context.push(canvaslst[i].getContext('2d'));
  }

/**
 * Get page info from document, resize canvas accordingly, and render page.
 * @param num Page number.
 */
function renderPage(num) {
  var index = (num - 1) % 10;
  var canvas = canvaslst[index];
  var ctx = context[index];
  if (num <= pdfDoc.numPages) {
    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;
        }
      });
    });
  } else {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
  }

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

/**
 * If another page rendering in progress, waits until the rendering is
 * finised. Otherwise, executes rendering immediately.
 */
function queueRenderPage(num) {
  if (pageRendering) {
    pageNumPending = num;
  } else {
    for (var i = 0; i < 10; i++)
      renderPage(num + i);
  }
}

/**
 * Displays previous...