Since Angular 8, the CLI has transformed decorator metadata to a form that can be used by the Angular dependency injector without the TDZ limitations of Typescript's decorator metadata emit feature.
As a result, a JIT application compiled with the CLI no longer requires the reflect metadata polyfill that was provided by `core-js`.
This polyfill was also the last remaining usage of the `core-js` package within `@angular-devkit/build-angular` which allows the `core-js` package to also be removed.
Refs: https://github.com/angular/angular-cli/pull/14473 & https://github.com/angular/angular/pull/37382
BREAKING CHANGE: Reflect metadata polyfill is no longer automatically provided in JIT mode
Reflect metadata support is not required by Angular in JIT applications compiled by the CLI.
Applications built in AOT mode did not and will continue to not provide the polyfill.
For the majority of applications, the reflect metadata polyfill removal should have no effect.
However, if an application uses JIT mode and also uses the previously polyfilled reflect metadata JavaScript APIs, the polyfill will need to be manually added to the application after updating.
To replicate the previous behavior, the `core-js` package should be manually installed and the `import 'core-js/proposals/reflect-metadata';` statement should be added to the application's `polyfills.ts` file.
With this change we update the TypeScript compilation target to `ES2020` for both new and existing projects. This is because all browsers that Angular supports (https://angular.io/guide/browser-support) support `ES2020` features without the need for polyfills.
rxjs 6 requires directory imports which are not support in ES modules. Disabling `fullySpecified` allows Webpack to ignore cases such as this until the package can be updated to use package exports.
With Webpack 5, the `raw-loader` is no longer needed and its functionality is provided via configuration options within the Webpack configuration via asset modules. Asset modules (https://webpack.js.org/guides/asset-modules/) provide a built-in way to provide `raw-loader`, `url-loader`, and `file-loader` functionality without additional dependencies.
With this change we update the target and module settings of various compilation units.
- We replace ES5 target in protractor. Protractor runs on Node.Js which support ES2018
- For applications we now use `ES2020` instead of `ESNext` as a module to avoid unexpected changes in behaviour
This changes also adds a migration to update existing projects and also removes `module` from the Universal tsconfig as per #17352 to enable lazy loading on the server.
