I would like to observe whenever a property of a third party object is changed. I'm taking the approach of assigning a custom setter but my console.log below is never invoked. Why is that? Is there a better approach?

const foo = { a: 1, b: 2 };

Object.assign(foo, {
  set user(user) {
    foo.user = user;
    console.log(">>>>>> user was changed", user);
  },
});

foo.user = "asdf";

Please note, I need to mutate foo I cannot wrap a proxy around foo and return that because it is a third party library which sets .user internally

CodePudding user response：

I've found a way, pretty hacky as it is

const foo = { a: 1, b: 2 };

let underlyingValue = foo.user

Object.defineProperty(foo, "user", {
  get() {
    return underlyingValue
  },
  set(user) {
    underlyingValue = user;
    console.log(">>>>>> user was changed", user);
  },
  enumerable: true,
  configurable: false
});

foo.user = "asdf";
console.log(foo)

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I've made this into a generic function below