Implement alternative location for PDF.js

@@ -8,6 +8,7 @@
 - Output image sized to cropBox instead of mediaBox (iOS) [garrettApproachableGeek]
 - Replace Activity with Context for Service Compatibility (Android) [Heinrich]
 - Deprecate support for `convertHtml`
+- Implement alternative location for PDF.js [Aleksei]
 
 ## 5.11.1
 

@@ -43,7 +43,7 @@ for documentation.
    <true/>
    ```
 
-5. If you want to manually set the PdfJs library version for the web, a small script
+5. If you want to manually set the Pdf.js library version for the web, a small script
    has to be added to your `web/index.html` file, just before `</head>`.
    Otherwise it is loaded automatically:
 
@@ -52,6 +52,20 @@ for documentation.
      var dartPdfJsVersion = "3.2.146";
    </script>
    ```
+    5.1. If you want to manually set the alternative location for loading Pdf.js library for the web, the following script has to be added to your `web/index.html` file, just before `</head>`.
+
+    ```html
+    <script>
+      var dartPdfJsBaseUrl = "https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.2.146/";
+    </script>
+   ```
+    It is possible to use local directory which will be resolved to the host where the web app is running.
+
+    ```html
+    <script>
+      var dartPdfJsBaseUrl = "assets/js/pdf/3.2.146/";
+    </script>
+   ```
 
 6. For Windows and Linux, you can force the pdfium version and architecture
    on your main `CMakeLists.txt` with:

@@ -33,6 +33,9 @@ import 'src/printer.dart';
 import 'src/printing_info.dart';
 import 'src/raster.dart';
 
+const _dartPdfJsVersion = 'dartPdfJsVersion';
+const _dartPdfJsBaseUrl = 'dartPdfJsBaseUrl';
+
 /// Print plugin targeting Flutter on the Web
 class PrintingPlugin extends PrintingPlatform {
   /// Registers this class as the default instance of [PrintingPlugin].
@@ -51,14 +54,11 @@ class PrintingPlugin extends PrintingPlatform {
   final _loading = Mutex();
 
   bool get _hasPdfJsLib => js.context.callMethod('eval', <String>[
-        'typeof pdfjsLib !== "undefined" && pdfjsLib.GlobalWorkerOptions.workerSrc!="";'
+        'typeof pdfjsLib !== "undefined" && pdfjsLib.GlobalWorkerOptions.workerSrc != "";'
       ]);
 
-  String get _selectPdfJsVersion => js.context.hasProperty('dartPdfJsVersion')
-      ? js.context['dartPdfJsVersion']
-      : _pdfJsVersion;
-
-  String get _pdfJsUrlBase => '$_pdfJsCdnPath@$_selectPdfJsVersion/';
+  /// The base URL for loading pdf.js library
+  late String _pdfJsUrlBase;
 
   Future<void> _initPlugin() async {
     await _loading.acquire();
@@ -86,10 +86,21 @@ class PrintingPlugin extends PrintingPlatform {
       }
       js.context['module'] = 0;
 
+      // Check if the source of PDF.js library is overridden via
+      // [dartPdfJsBaseUrl] JavaScript  variable.
+      if (js.context.hasProperty(_dartPdfJsBaseUrl)) {
+        _pdfJsUrlBase = js.context[_dartPdfJsBaseUrl] as String;
+      } else {
+        final pdfJsVersion = js.context.hasProperty(_dartPdfJsVersion)
+            ? js.context[_dartPdfJsVersion]
+            : _pdfJsVersion;
+        _pdfJsUrlBase = '$_pdfJsCdnPath@$pdfJsVersion/build/';
+      }
+
       final script = html.ScriptElement()
         ..type = 'text/javascript'
         ..async = true
-        ..src = '$_pdfJsUrlBase/build/pdf.min.js';
+        ..src = '${_pdfJsUrlBase}pdf.min.js';
       assert(html.document.head != null);
       html.document.head!.append(script);
       await script.onLoad.first;
@@ -100,7 +111,7 @@ class PrintingPlugin extends PrintingPlatform {
       }
 
       js.context['pdfjsLib']['GlobalWorkerOptions']['workerSrc'] =
-          '$_pdfJsUrlBase/build/pdf.worker.min.js';
+          '${_pdfJsUrlBase}pdf.worker.min.js';
 
       // Restore module and exports
       if (module != null) {