函数参数和对象

Question

function f(o) {
  o.message = "set in f";
  o = {
    message: "new object!"
  };
  console.log(`inside f: o.message="${o.message}" (after assignment)`);
}
let o = {
  message: 'initial value'
};
console.log(`before calling f: o.message="${o.message}"`);
f(o);
console.log(`after calling f: o.message="${o.message}"`);

如果运行此示例，您将看到：

before calling f: o.message="initial value"
inside f: o.message="new object!" (after assignment)
after calling f: o.message="set in f"

我正在阅读学习javascript的书，而且我不理解这段代码，尤其是console.log中的代码确实令人困惑。

谢谢。