Actually == true and == false will still work, === true and === false will fail (as the return value is now "disabled" or undefined).

I meant, explicit checks on the return value will break (not that this is a bad thing). Specifically, neither `'disabled' == true` nor `undefined == false` will ever be true[thy] and are thus breaking changes.

Perhaps you meant implicit conversions to boolean still working? Eg `!!'disabled'`, `if ('disabled')`, `!!undefined`, or `if (undefined)` will continue to work.