Support almond.js

[iloire]

Configuration:

• Web browser and its version: This problem can be reproduced in IE 11, when PDF.js is loaded from a different origin (CDN).
• Operating system and its version: Windows 7
• PDF.js version: 1.4.215

If PDF.js is loaded from a CDN and fail safe mode is triggered (hence making PDF.js trying to initialise a fake worker), if the current AMD loader is almond.js instead of requirejs, loading pdf.worker.js will fail since almond.js does not support dynamic script loading.

This is the code where the exception is thrown:

var fakeWorkerFilesLoader = useRequireEnsure ? (function (callback) {
  require.ensure([], function () {
    var worker = require('./pdf.worker.js');
    callback(worker.WorkerMessageHandler);
  });
}) : (typeof requirejs !== 'undefined') ? (function (callback) {

  // THIS WILL FAIL IF THE CURRENT AMD LOADER IS ALMOND.JS INSTEAD OF REQUIRE.JS 
  requirejs(['pdfjs-dist/build/pdf.worker'], function (worker) {
    callback(worker.WorkerMessageHandler);
  });
}) : null;

One potential solution would be to only dynamic load the dependency if the AMD loader supports it:

}) : (typeof requirejs !== 'undefined' && requirejs.load) ? (function (callback) { 

instead of

}) : (typeof requirejs !== 'undefined') ? (function (callback) { 

This change will set fakeWorkerFilesLoader to null when the ADM loader does not support dynamic loading and worker.js will be loaded using Util.loadScript instead:

      var loader = fakeWorkerFilesLoader || function (callback) {
        Util.loadScript(getWorkerSrc(), function () {
          callback(window.pdfjsDistBuildPdfWorker.WorkerMessageHandler);
        });
      };

[iloire]

Raised a PR for this:
#7185

[yurydelendik]

Fixed by #7185