function test(x) {
  let _x;

  _x = x;

  class F {
    constructor() {
      this[_x] = 1;
    }

  }

  x = 'deadbeef';
  expect(new F().foo).toBe(1);
  x = 'wrong';
  expect(new F().foo).toBe(1);
}

test('foo');