Support PDF.js >= 2.5.207

Since [1] PDF.js does not dispatch events to the DOM any more. Therefore
the client needs to listen for the `documentloaded` event from
`PDFApplicationViewer.eventBus`. The `eventBus` property is only
available once the viewer is initialized, so the client needs to wait
for `initializedPromise` to resolve before checking it.

[1] mozilla/pdf.js#11655

Author: robertknight

src/annotator/plugin/pdf-metadata.js

@@ -42,19 +42,32 @@ export default class PDFMetadata {
       const finish = () => {
         window.removeEventListener('documentload', finish);
         window.removeEventListener('documentloaded', finish);
+        app.eventBus?.off('documentloaded', finish);
+
         resolve(app);
       };
 
       if (app.downloadComplete) {
         resolve(app);
       } else {
-        // Listen for either the `documentload` (older PDF.js) or
-        // `documentloaded` (newer PDF.js) events which signal that the document
+        // Listen for "documentloaded" event which signals that the document
         // has been downloaded and the first page has been rendered.
-        //
+
+        // Newer versions of PDF.js (>= v2.5.207) report events only via
+        // the PDFViewerApplication's own event bus.
+        app.initializedPromise?.then(() => {
+          app.eventBus?.on('documentloaded', finish);
+        });
+
+        // Older versions of PDF.js (< v2.5.207) dispatch events to the DOM
+        // instead or as well.
+
+        // PDF.js >= v2.0.943.
         // See https://github.com/mozilla/pdf.js/commit/7bc4bfcc8b7f52b14107f0a551becdf01643c5c2
-        window.addEventListener('documentload', finish);
         window.addEventListener('documentloaded', finish);
+
+        // PDF.js < v2.0.943.
+        window.addEventListener('documentload', finish);
       }
     });
   }

src/annotator/plugin/test/pdf-metadata-test.js

@@ -1,3 +1,5 @@
+import EventEmitter from 'tiny-emitter';
+
 import PDFMetadata from '../pdf-metadata';
 
 /**
@@ -41,11 +43,22 @@ class FakePDFViewerApplication {
    * Initialize the "PDF viewer" as it would be when loading a document or
    * when a document fails to load.
    */
-  constructor(url = '') {
+  constructor(url = '', { domEvents = false, eventBusEvents = true } = {}) {
     this.url = url;
     this.documentInfo = undefined;
     this.metadata = undefined;
     this.pdfDocument = null;
+    this.dispatchDOMEvents = domEvents;
+
+    // Use `EventEmitter` as a fake version of PDF.js's `EventBus` class as the
+    // API for subscribing to events is the same.
+    if (eventBusEvents) {
+      this.eventBus = new EventEmitter();
+    }
+
+    this.initializedPromise = new Promise(resolve => {
+      this._resolveInitializedPromise = resolve;
+    });
   }
 
   /**
@@ -58,10 +71,6 @@ class FakePDFViewerApplication {
     title,
     eventName = 'documentload',
   }) {
-    const event = document.createEvent('Event');
-    event.initEvent(eventName, false, false);
-    window.dispatchEvent(event);
-
     this.url = url;
     this.downloadComplete = true;
     this.documentInfo = {};
@@ -75,29 +84,69 @@ class FakePDFViewerApplication {
     }
 
     this.pdfDocument = new FakePDFDocumentProxy({ fingerprint });
+
+    if (this.dispatchDOMEvents) {
+      const event = document.createEvent('Event');
+      event.initEvent(eventName, false, false);
+      window.dispatchEvent(event);
+    }
+    this.eventBus?.emit(eventName);
   }
+
+  /**
+   * Simulate PDF viewer initialization completing.
+   *
+   * At this point the event bus becomes available.
+   */
+  completeInit() {
+    this._resolveInitializedPromise();
+  }
+}
+
+function delay(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
 }
 
 describe('annotator/plugin/pdf-metadata', function () {
   [
-    // Event dispatched in older PDF.js versions (pre-7bc4bfcc).
-    'documentload',
-    // Event dispatched in newer PDF.js versions (post-7bc4bfcc).
-    'documentloaded',
-  ].forEach(eventName => {
-    it('waits for the PDF to load before returning metadata', function () {
-      const fakeApp = new FakePDFViewerApplication();
+    {
+      // Oldest PDF.js versions (pre-2.x)
+      eventName: 'documentload',
+      domEvents: true,
+      eventBusEvents: false,
+    },
+    {
+      // Newer PDF.js versions (~ < 2.5.x)
+      eventName: 'documentloaded',
+      domEvents: true,
+      eventBusEvents: false,
+    },
+    {
+      // Current PDF.js versions (>= 2.5.x)
+      eventName: 'documentloaded',
+      domEvents: false,
+      eventBusEvents: true,
+    },
+  ].forEach(({ eventName, domEvents = false, eventBusEvents = false }, i) => {
+    it(`waits for PDF to load (${i})`, async () => {
+      const fakeApp = new FakePDFViewerApplication('', {
+        domEvents,
+        eventBusEvents,
+      });
       const pdfMetadata = new PDFMetadata(fakeApp);
 
+      fakeApp.completeInit();
+
+      // Give `PDFMetadata` a chance to register the "documentloaded" event listener.
+      await delay(0);
+
       fakeApp.finishLoading({
         eventName,
         url: 'http://fake.com',
         fingerprint: 'fakeFingerprint',
       });
 
-      return pdfMetadata.getUri().then(function (uri) {
-        assert.equal(uri, 'http://fake.com/');
-      });
+      assert.equal(await pdfMetadata.getUri(), 'http://fake.com/');
     });
   });
 

src/types/pdfjs.js

@@ -67,17 +67,30 @@
  * @prop {(page: number) => PDFPageView|null} getPageView
  */
 
+/**
+ * Defined in `web/ui_utils.js` in the PDF.js source.
+ *
+ * @typedef EventBus
+ * @prop {(event: string, listener: Function) => void} on
+ * @prop {(event: string, listener: Function) => void} off
+ */
+
 /**
  * The `PDFViewerApplication` global which is the entry-point for accessing PDF.js.
  *
  * Defined in `web/app.js` in the PDF.js source.
  *
  * @typedef PDFViewerApplication
+ * @prop {EventBus} [eventBus] -
+ *   Global event bus. Since v1.6.210.
  * @prop {PDFDocument} pdfDocument
  * @prop {PDFViewer} pdfViewer
  * @prop {boolean} downloadComplete
  * @prop {PDFDocumentInfo} documentInfo
  * @prop {Metadata} metadata
+ * @prop {Promise<void>} [initializedPromise] -
+ *   Promise that resolves when PDF.js is initialized. Since v2.4.456.
+ *   See https://github.com/mozilla/pdf.js/wiki/Third-party-viewer-usage#initialization-promise.
  */
 
 /**