by Sai gowtham

How to deep watch an array of objects in Vue.js

Home » vuejs » How to deep watch an array of objects in Vue.js

In this tutorial, we are going to learn about how to watch an array of objects in Vue.js with the help of examples.

Consider we have an array of objects like this.

const  users = [
        { id: 1, name: "John" },
        { id: 2, name: "seal" },
        { id: 3, name: "king" }
      ]

Now we need to watch any change happens in each object of a users array.

Getting started

First, we need to create a new component called User.vue where it handles each user data.

User.vue
<template>
  <p>{{user.id}}: <input v-model="user.name"></p></template>

<script>
export default {
  props: ["user"]};
</script>

Now, let’s use the above component by passing a users array data inside the App.vue file.

App.vue
<template>
  <div id="app">
    <div v-for="user in users" :key="user.id">
      <User :user="user"/>    </div>
  </div>
</template>

<script>
import User from "./components/User";

export default {
  name: "App",
  data() {
    return {
      users: [
        { id: 1, name: "John" },
        { id: 2, name: "seal" },
        { id: 3, name: "king" }
      ]
    };
  },
  components: {
    User
  }
};
</script>

Now, we need to detect any change happens on each user inside the User.vue component.

User.vue
<template>
  <p>{{user.id}}: <input v-model="user.name"></p>
</template>

<script>
export default {
  props: ["user"],
  watch: {
    "user.name": function(newVal, previousVal) {      console.log("new Value is " + newVal,       "previous value is " + previousVal);    }  }
};
</script>

In the above code, we have used "user.name" property instead of user so that vue can detect any change happens in the user.name property.

Let’s test it.

logging watch values

Similarly, you can also watch objects by adding deep: true but in that case, we didn’t get any previous value.

User.vue
<template>
  <p>{{user.id}}: <input v-model="user.name"></p>
</template>

<script>
export default {
  props: ["user"],
  watch: {
    user: {
    handler:function(newVal) {
      console.log("new Value is " + newVal)    },
     deep:true    },

  }
};
</script>