Vue监听属性 — watch

watch: {
  num(newVal, oldVal) {
    // newVal 变量num改变后的值
    // newVal 变量num改变前的值
    // 当变量num发生改变，执行当前回调
  },
},
data() {
  return {
    num: 1,
  };
}

watch: {
  site(newVal, oldVal) {
    // newVal 计算属性site计算后的值
    // newVal 计算属性site计算前的值
    // 当计算属性site的计算结果发生改变，执行当前回调
  },
},
computed: {
  site: {
    get() {
      return this.num;
    },
  },
},

watch: {
  obj: {
    handler(newVal, oldVal) {
      console.log("newVal ===>>>", newVal);
      console.log("oldVal ===>>>", oldVal);
    },
    deep: true,
  },
},
data() {
  return {
    obj: {
      name: "张三",
      sex: "18",
    },
  };
}

watch: {
  obj: {
    handler(newVal, oldVal) {
      console.log("newVal ===>>>", newVal);
      console.log("oldVal ===>>>", oldVal);
    },
    deep: true,
    immediate: true,
  },
}