watch

常见问题

watch监听响应式对象时出现新旧值一致问题

Vue3 写法：

state = reactive({ item: 1 });
let newState = computed(() => {
  return JSON.parse(JSON.stringify(state));
});
watch(
  newState,
  (newVal, oldVal) => {
    console.log(oldVal, "oldVal");
    console.log(newVal, "newVal");
  }
);

Vue2 写法：

computed: {
  newState() {
	return JSON.parse(JSON.stringify(this.state));
  }
},
watch: {
  newState:{
	handler: function(newVal, oldVal) {
	    console.log(oldVal, "oldVal");
	    console.log(newVal, "newVal");
	},
	deep: true
  },
},