Angular 9 fails to load pdfjs (v. 2.8.335) module with optional chaining

Question

I'm trying to update pdfjs module to the next version (2.8.335) in my Angular application and got following error:

ERROR in C:/project/node_modules/pdfjs-dist/build/pdf.js 2205:45
Module parse failed: Unexpected token (2205:45)
You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See https://webpack.js.org/concepts#loaders
|         intent: renderingIntent,
|         renderInteractiveForms: renderInteractiveForms === true,
>         annotationStorage: annotationStorage?.serializable || null
|       });
|     }
ERROR in C:/project/node_modules/pdfjs-dist/web/pdf_viewer.js 613:31
Module parse failed: Unexpected token (613:31)
You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See https://webpack.js.org/concepts#loaders
|   _cachedPageNumber(pageRef) {
|     const refStr = pageRef.gen === 0 ? `${pageRef.num}R` : `${pageRef.num}R${pageRef.gen}`;
>     return this._pagesRefCache?.[refStr] || null;
|   }

This problem is related to version of webpack used by @angular-devkit/[email protected], I use the latest version available for Angular 9. This version of build-angular uses [email protected] which triggers these errors. I found that optional chaining and null-coalescing are supported out of box in webpack higher than 5 ver, but I'm limited with Angular 9 and cannot update it to higher version to load build-angular and as dependency, webpack to higher version.

Is there a way to configure webpack to support optional chaining and null-coalescing features of js in order to load the module into my application?

There is a way to "eject" webpack configuration ng eject, thus you would be able to edit it manually. — Akxe
– Akxe, Commented May 26, 2021 at 18:31
Thank you, that helped to catch the idea that make my app work! — Valentine
– Valentine, Commented May 26, 2021 at 21:00

Akxe · Accepted Answer · 2021-05-28 19:10:23Z

With hint from Akxe I managed to solve the issue in following way:

@angular-devkit/build-angular has builder @angular-builders/custom-webpack:dev-server described here. I added this builder to angular.json file at my project like this:

...
"serve": {
  "builder": "@angular-builders/custom-webpack:dev-server",
  "options": {
    "browserTarget": "myApp:build",
    "proxyConfig": "apps/myApp/proxy.conf.js",
    "customWebpackConfig": {
      "path": "apps/myApp/webpack.config.js"
    }
  },
...

if file webpack.config.js I added babel loader with filter to load only files from pdfjs-dist:

module.exports = {
  module: {
    rules: [
      {
        test: /\.*pdfjs-dist.*$/,
        use: {
          loader: 'babel-loader',
          options: {
            presets: ['@babel/preset-env']
          }
        }
      }
    ]
  }
};

This configuration allows to transpile es2020 module of pdfjs to earlier version of js which easily consumed by standard webpack configuration, defined by angular under the hood.

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