Missing Automatic Polyfills as Described in Docs

[Char2sGu]

Command

build

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

v8?

Description

As described at https://angular.dev/tools/cli/build#configuring-browser-compatibility, polyfills should be automatically added based on the browserslist configuration:

The Angular CLI uses Browserslist to ensure compatibility with different browser versions. Depending on supported browsers, Angular will automatically polyfill and transform certain JavaScript and CSS features to ensure the built application does not use a feature which has not been implemented by a supported browser.

Angular V8 used to add core-js polyfills automatically according to StackOverflow discussions at https://stackoverflow.com/questions/56892243/is-not-core-js-needed-anymore:

The difference with core-js in ng8 is that, since the CLI is handling polyfills, core-js is a dependency of the CLI. So even if you uninstall core-js as part of upgrading to ng8, you'll see it's still in your node_modules folder, but you won't have to manage which version is installed.

However, currently no core-js dependencies are found and also no core-js polyfills are automatically added. Angular CLI uses @babel/preset-env when building Angular applicaitons, which has built-in support of automatic polyfilling based on core-js, but this feature is not enabled:

https://github.com/angular/angular-cli/blob/c7205ea182f6c38231ce8fe8ab358dc7eab58d65/packages/angular_devkit/build_angular/src/tools/babel/presets/application.ts#L215-L224

Minimal Reproduction

N/A

Exception or Error

No response

Your Environment

Angular CLI: 17.3.0
Node: 18.19.0
Package Manager: npm 10.2.3
OS: linux x64

Angular: 17.3.0
... animations, cdk, cli, common, compiler, compiler-cli, core
... elements, forms, localize, material, platform-browser
... router, service-worker

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1703.0
@angular-devkit/build-angular   17.3.0
@angular-devkit/core            17.3.0
@angular-devkit/schematics      17.3.0
@schematics/angular             17.3.0
rxjs                            7.8.1
typescript                      5.2.2
zone.js                         0.14.2

Anything else relevant?

No response

[alan-agius4]

The docs are incorrect here as the Angular CLI does not add polyfills.

See: angular/angular-cli#27510

[Char2sGu]

Alright then. I understand the design concerns, although do not fully agree.
Did any previous Angular version ever support automatic polyfills? According to historical community discussions, automatic polyfilling was once supported.

[alan-agius4]

No we never supported automatic polyfilling.

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