When a class includes an iterator method using Symbol.iterator, it is no longer tree-shaken when unused.

(() => {
  class Test {
    *[Symbol.iterator]() {
      // do nothing
    }
  }
})()

Example

If you change this to *foo (still a generator function), or a non-generator with a static identifier as a name, it is tree-shaken. I believe this should be safe to tree shake with Symbol.iterator as well. SWC's minifier does so.