Global Scope in Javascript Variable Not working as expected

Question

<html>
<body>
  <div>
    <button id="prev" onclick="goPrevious()">Previous</button>
    <button id="next" onclick="goNext()">Next</button>
    &nbsp; &nbsp;
    <span>Page: <span id="page_numo"></span> / <span id="page_count"></span></span>
    <input type=text id="elNum" value=1>

  </div>

  <div>
    <canvas id="the-canvas" style="border:0px solid black"></canvas>
  </div>

  <!-- Use latest PDF.js build from Github -->
  <script type="text/javascript" src="https://raw.github.com/mozilla/pdf.js/gh-pages/build/pdf.js"></script>

  <script type="text/javascript">
    //
    // NOTE: 
    // Modifying the URL below to another server will likely *NOT* work. Because of browser
    // security restrictions, we have to use a file server with special headers
    // (CORS) - most servers don't support cross-origin browser requests.
    //
    var url = 'http://cdn.mozilla.net/pdfjs/tracemonkey.pdf';

    //
    // Disable workers to avoid yet another cross-origin issue (workers need the URL of
    // the script to be loaded, and currently do not allow cross-origin scripts)
    //
    PDFJS.disableWorker = true;

    var pdfDoc = null,
        pageNum = 1,
        scale = 0.8,
        canvas = document.getElementById('the-canvas'),
        ctx = canvas.getContext('2d');





    //
    // Get page info from document, resize canvas accordingly, and render page
    //
    function renderPage(num) {
      // 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
        };
        page.render(renderContext);
      });

      // Update page counters
      document.getElementById('page_numo').textContent = pageNum;
      document.getElementById('page_count').textContent = pdfDoc.numPages;
      sic = document.getElementById('elNum');
      sic.value = pageNum;
    }

   crc = 1;
    //



    // Go to previous page
    //

    function goPrevious() {
      if (pageNum <= 1)
        return;
      pageNum--;
      crc = pageNum;      
      renderPage(pageNum);
    }

    //
    // Go to next page
    //
    function goNext() {
      if (pageNum >= pdfDoc.numPages)
        return;
      pageNum++;
      crc = pageNum;
      renderPage(pageNum);
    }

    //
    // Asynchronously download PDF as an ArrayBuffer
    //
    PDFJS.getDocument(url).then(function getPdfHelloWorld(_pdfDoc) {
      pdfDoc = _pdfDoc;
      renderPage(pageNum);
    });
   document.write ('Current page is '+crc);
    </script>

</body>
</html>

That's the code. It's the simplest version of an online pdf renderer (pdf.js). I've been working on a project which needs to pass the pageNum (The current pdf page number) variable via url to another script for process. But the problem is I haven't been by no way able to retrieve pageNum value outside the renderPage function. I think it's matter of Javascript Variable Scopes but cannot see what's wrong with my attempt to extract via the crc variable or via document.getElementById('elNum').value... (See the document.write ('Current page is '+crc); line at the end of the script and the field in 8th line to see how I have been trying to retrieve the value).

Anybody can give me any clues about what am I doing wrong? Test page Here (http://jsbin.com/pdfjs-prevnext-v2/2091/edit)

Note: I have seen other questions on this topic but this seems to be a weird case. Really need some help and hopefully someone else will need it in the future.

vn_grv · Accepted Answer · 2013-03-19 03:41:36Z

0

document.write ('Current page is '+crc) executed only when the page is loaded. crc-is a global variable and can be used.

    var viewCurrPage = function() {
        console.log('Current page is '+crc);
    };

    function goPrevious() {
          if (pageNum <= 1)
            return;
          pageNum--;
          crc = pageNum;      
          renderPage(pageNum);
          viewCurrPage();
        };

function goNext() {
      if (pageNum >= pdfDoc.numPages)
        return;
      pageNum++;
      crc = pageNum;
      renderPage(pageNum);
      viewCurrPage();
    }

answered Mar 19, 2013 at 3:41

vn_grv

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2 Comments

Boris Javier Barrera Over a year ago

Yeah, thanks for your answer, that's great! But i can't figure out how to pass variable crc via url to another page for process, for instance: document.write('<a href=\'process.php?page='+crc+'\'>Page to process is '+crc+'</a>'); Any ideas?

vn_grv Over a year ago

document.write - not the best variant for this. You need to create a function that changes the global var crc. After you need Dynamically Create Link Javascript see here for an example stackoverflow.com/questions/9831074/…

Boris Javier Barrera · Accepted Answer · 2013-03-24 01:19:19Z

0

This, combined with the simple function by vn_grv could be useful

var viewCurrPage = function() {
        //console.log('Current page is '+crc);
      document.getElementById('one').innerHTML = '<a href="process.php?page='+crc+'">Process page '+crc+'</a>';
    };
//Simply adding the corresponding div like: 
<div id="one"></div>

Thanks for your answer. Best regards,

answered Mar 24, 2013 at 1:19

Boris Javier Barrera

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