this指向问题

window.b = 1;
function fn () {
  console.log(this.b);
}
const fn2 = () => {
  console.log(this.b);
}
const a = {
  b: 2,
  k: () => {
    return fn();
  },
  o: function () {
    return fn();
  },
  l: () => {
    return fn2();
  },
  p: function () {
    return fn2();
  },
  j: () => {
    fn.call(this);
  },
  u: function () {
    fn.call(this);
  }
}
a.k();
a.o();
a.l();
a.p();
a.j();
a.u();