vue正确使用watch监听属性变化方式

<template>
  <input type="number" v-model.number="counter" />
</template>

<script>
export default {
  name: "Counter",
  data: function() {
    return {
      counter: 0,
    };
  },
  watch: {
    counter: function(newV, oldV) {
      console.log('counter change to %d from %d', newV, oldV);
    },
  }
};
</script>

<template>
  <div>
    <label>up trigger {{ counter.up }} times</label>
    <button @click="onTrigger('up')">Trigger Up</button>
    <br>
    <label>down trigger {{ counter.down }} times</label>
    <button @click="onTrigger('down')">Trigger down</button>
  </div>
</template>

<script>
export default {
  name: "Counter",
  data: function() {
    return {
      counter: {
        up: 0,
        down: 0,
      },
    };
  },
  methods: {
    onTrigger: function(type) {
      this.counter[type] += 1;
    }
  },
  watch: {
    counter: function(newV, oldV) {
      // 不会被触发
      console.log('counter change to %o from %o', newV, oldV);
    },
  }
};
</script>

watch: {
  counter: {
    handler: function(newV, oldV) {
      console.log('counter change to %o from %o', newV, oldV);
    },
    deep: true,
  }
}

methods: {
  onTrigger: function(type) {
    // 重新赋值触发变化
    this.counter = {
      ...this.counter,
      [type]: this.counter[type] + 1,
    };
  }
},
watch: {
  counter: function(newV, oldV) {
    // 不会被触发
    console.log('counter change to %o from %o', newV, oldV);
  },
}

watch: {
  'counter.up': function(newV, oldV) {
    console.log('counter.up change to %d from %d', newV, oldV);
  },
  'counter.down': function(newV, oldV) {
    console.log('counter.down change to %d from %d', newV, oldV);
  },
}

watch: {
  counter: {
    handler: function(newV, oldV) {
      console.log('counter change to %o from %o', newV, oldV);
    },
    immediate: true,
  }
}