Problem/Motivation
Based on discussion during Drupal Dev Days between @lauriii, @nod_, and @justafish, the build tooling is no longer needed in Drupal 10 due to wide enough support for ES6 features in browsers. However, the tooling is used widely by contrib ecosystem even though it was never designed for that use case, and was explicitly marked as internal.
Proposed resolution
Deprecate core/scripts/js/babel-es6-build.js for removal from 10.0.x
Remaining tasks
User interface changes
API changes
Data model changes
Release notes snippet
The JavaScript ES6 build process is removed given that all browsers supported by Drupal Core are now ES6 compatible. This means that once the build tooling is removed from Drupal 10, core developers are no longer required to run the commands when they make changes to core JavaScript. This also means that babel/core and all related dependencies will no longer be included as core development dependencies.