When does the TS compiler output EMCAScript Private Fields using WeakMaps?

Question

I'm aware that the TypeScript compiler can use a workaround via WeakMap to "polyfill" ECMAScript Private class fields, but when does/doesn't it do that?

Answer 1

According to the official documentation, the TypeScript compiler uses WeakMaps when the target output is configured to ES2021 or less, and otherwise outputs ECMAScript private class fields.