How to evaluate Vue.js component props in the data property?

Question

I have 2 components: Post and Comments.

Inside Post component, there is Comments component that has 3 props: postId, numCom (number of comments) and comments (array).

I get comments and I pass the array with props, and now I want to retrieve the array in Comments component and add it to data so I can then add/remove comments etc.

Here is my code in Comments.vue:

props: ['id', 'numCom', 'comments'],
data: function() {
  return {
     newMessage: "",
     loading: false,
     allComments: this.comments,
     num: this.numCom,
   }
},

But this doesn't works. In Vue developer tools I can see that comments prop is filled with comments, but allComments array is empty.

What should I do?

Answer 1

It looks like the comments prop does not have a value at the time of the component's creation (which is the only time allComments will be set).

You can either:

1. Defer the creation of the component until the comments prop is ready by using v-if like this:

<comments v-if="comments" :comments="comments"></comments>

2. Watch for changes to the comments prop and set allComments to the new value (in addition to initializing allComments in the data function):

watch: {
  comments(value) {
    this.allComments = value;
  }
}