babel/packages/babel-plugin-transform-class-properties/test/fixtures/private/instance/exec.js

class Foo {
  #bar = "foo";

  test() {
    return this.#bar;
  }

  update() {
    this.#bar++;
  }

  set(val) {
    this.#bar = val;
  }

  static test(foo) {
    return foo.#bar;
  }

  static update(foo) {
    foo.#bar **= 2;
  }
}

const f = new Foo();
expect(f.test()).toBe("foo");
expect(Foo.test(f)).toBe("foo");
expect("bar" in f).toBe(false);

f.set(1);
expect(f.test()).toBe(1);
f.update();
expect(Foo.test(f)).toBe(2);
Foo.update(f);
expect(f.test()).toBe(4);