ESM is the closest to a major version for JS. It forces strict mode, which includes many non-backwards compatible changes [0]. Most notably, it removes the `with` statement. Other examples of removals are octal literals or assignments to undeclared variables.
Yep, it's going to take time but eventually one day the vast majority of JS code in the wild will be strict mode and the non-strict stuff will be de facto deprecated and not expected to work everywhere
[0]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...