How to know which function trigger watch handler?

after click changeName or changeAge,both of them will trigger user’s handler,how can I know which
function trigger the handler ?

    <button @click="changeName">change name</button>
    <button @click="changeAge">change age</button>

export default {
  methods: {
    changeName() { = 'bar';
    changeAge() { = 20;
  data() {
    return {
      user: {
        name: "foo",
        age: 18
  watch: {
    user: {
      deep: true,
      handler() {
        console.log('user change');

callstack in this example has related informatinos.

but int my project, only has flushCallbacks and later

Don’t just watch the user object as a whole, watch each property individually.

The other option could be to compare the returned val and oldVal values

I want to know where trigger the handler, compare the returned val and oldVal values doesn’t help.