How to suppress “Undefined” errors before fetching

问题:

I have a simple page where I display some data that are fetched from the server.

Template:

<p>Order's customer name: {{ order.customer.name }}</p>

Javascript:

export default {
    data () { return { order: {} } },
    mounted () { this.fetchOrder() },
    methods: {
        fetchOrder () {
            /* get the order data asynchronously from the server */
            .success(function () { this.order = data_from_server })
        }
    }
}

Everything works just fine but in browser's console there is an error: "Cannot read property 'name' of undefined". Apparently the problem is that it takes some time to fetch the order data from the server and meanwhile it tries to access order.customer.name, which results in error, because order.customer is undefined.

How can I suppress this error? What's the best solution to this?

Of course, I can explicitly define the order structure (eg. order: { customer: {} }), but that doesn't seem nice to me, especially when the data structure grows to several-level-nested objects.

回答1:

new Vue({
  el: '#app',
  data: {
    data: {name: 'daniel'},
    data2: {}
  }
})

<script src="https://unpkg.com/vue"></script>

<div id="app">
  <p v-if="data" v-text="data.name"></p>
  <p v-if="data2" v-text="data2.name"></p>
</div>

You need to render it conditionally. Since data from the backend is not accessible from the very beginning, you should add a condition to display element only when the data is ready. See example.

<p>Order's customer name: <span v-if="order" v-text="order.customer.name"></span></p>

回答2:

I think you can test for order.customer :

{{ order.customer && order.customer.name }}

if order.customer is not defined, the expression evaluation will simply stop at the first term without throwing an error.

回答3:

You can use ternary operator to check

<p>Order's customer name: {{ order.customer?order.customer.name:'' }}</p>