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When using watch in Vue , you may need to monitor an object, but only care about certain properties in the object, not all properties of the object. In this case, you can use deep monitoring and calculated properties, or add some options to watch to exclude monitoring of certain properties.

1. Deep listening and calculated properties

Deep monitoring is a feature in Vue.js that monitors changes in object properties and recursively observes each property inside the object. You can use computed properties to filter out properties that do not need to be monitored, so that only the required operations are triggered.

Here is an example:

HTML Code

<div id="app">
  <span>{{obj.a}}</span>
  <button @click="update">update</button>
</div>

JS Code

new Vue({
  el: '#app',
  data: {
    obj: {a: 1, b: 2},
    c: 3
  },
  computed: {
    watchedObj() {
      return {a: this.obj.a};
    }
  },
  methods: {
    update() {
      this.obj.a++;
      this.obj.b++;
      this.c++;
    }
  },
  watch: {
    watchedObj: {
      handler(val, oldVal) {
        console.log('old:', oldVal);
        console.log('new:', val);
      },
      deep: true
    }
  }
});

In this example, we define an object obj and a computed property watchedObj, which contains only the properties we want to monitor. Then we monitor watchedObj in watch and set the deep option to true, so that watchedObj will be triggered only when obj.a changes.

2. Option Filter

In watch , you can use an options object to set some options, including immediate, deep, handler, etc. Another option is watch filtering, which can be used to exclude monitoring of certain attributes.

Here is an example:

HTML Code

<div id="app">
  <span>{{obj.a}}</span>
  <button @click="update">update</button>
</div>

JS Code

new Vue({
  el: '#app',
  data: {
    obj: {a: 1, b: 2},
    c: 3
  },
  methods: {
    update() {
      this.obj.a++;
      this.obj.b++;
      this.c++;
    }
  },
  watch: {
    obj: {
      handler(val, oldVal) {
        console.log('old:', oldVal);
        console.log('new:', val);
      },
      deep: true,
      // Here are the filter options
      watch(prop, val) {
        return prop === 'a';
      }
    }
  }
});

In this example, we use a new option watch in watchobj.a , whose value is a filter function. This function can receive two parameters: prop and val, which represent the property name and new value of the object respectively. In this example, we only monitor the changes of because the filter function only returns obj.a.

Summarize

When using watch in Vue , you can use deep monitoring and calculated properties, or add a filter function in watch to exclude monitoring of certain properties. Either method can help you monitor object properties more effectively.