What should I do if "Uncaught TypeError: Cannot read property 'xxx' of null" appears when using vue-resource in a Vue application?

When using vue-resource in a Vue application, we may encounter the error message "Uncaught TypeError: Cannot read property 'xxx' of null". This error message means that we The object or property you are trying to access is null or undefined. This error is very common, but it is difficult to locate the specific problem.

Let’s talk about the possible reasons and solutions for the error "Uncaught TypeError: Cannot read property 'xxx' of null" when using vue-resource in Vue applications.

1. Whether vue-resource is introduced correctly

We need to ensure that vue-resource is correctly introduced in the Vue application, otherwise there will be an inability to read methods or properties. mistake.

Use the following code in the HTML file to ensure that vue-resource has been introduced correctly:

<script src="https://cdn.jsdelivr.net/npm/vue-resource@latest/dist/vue-resource.min.js"></script>

Use npm to install vue-resource in the Vue project, and then introduce it in the main.js file:

import Vue from 'vue'
import VueResource from 'vue-resource'

Vue.use(VueResource);

2. Is vue-resource configured correctly

If we have introduced vue-resource correctly, then there may be a problem with our vue-resource configuration.

In the Vue project, we can configure vue-resource in the main.js file. For example, we can set the default request header information:

Vue.http.headers.common['Authorization'] = 'Bearer ' + token;

If we access it in the code An undefined property will cause the "Cannot read property 'xxx' of null" error mentioned above.

So we need to check our configuration carefully to ensure that all properties have been defined correctly.

3. Whether the related methods of vue-resource are used correctly

When using vue-resource in a Vue application, we can access vue-resource through this.$http Methods. But if we don’t use these methods correctly, the errors mentioned above will occur.

For example, if we use the get method but do not pass in the correct request parameters, then there will be an error that cannot read the attribute:

this.$http.get('https://example.com/api') // 请求不成功
    .then(response => {
        // code
    });

The correct way to use it should be to pass in the request Parameters:

this.$http.get('https://example.com/api', {params: {id: 1}}) // 请求成功
    .then(response => {
        // code
    });

4. Whether asynchronous operations are used correctly

There are usually asynchronous operations in Vue applications. These asynchronous operations may cause vue-resource related methods to not work properly. implement. For example:

created: function () {
  this.getItems();
},
methods: {
  getItems: function () {
    this.$http.get('https://example.com/api') // 发送异步请求
      .then(response => {
        this.items = response.data;
      });
  }
}

In this case, our getItems method is an asynchronous operation, which may cause the method to enter other code logic before it has completed execution. At this time, if we try to read the result before the asynchronous operation returns the result, the above error will occur.

We can avoid this error by using some judgment logic before the asynchronous operation:

created: function () {
  if (this.items.length === 0) { // 判断items 是否为空数组
    this.getItems();
  }
},
methods: {
  getItems: function () {
    this.$http.get('https://example.com/api') // 发送异步请求
      .then(response => {
        this.items = response.data;
      });
  }
}

In this case, we can avoid reading by judging whether items is an empty array. Take the wrong case.

Summary

When using vue-resource in a Vue application, an error like "Uncaught TypeError: Cannot read property 'xxx' of null" occurs. It may be because we did not introduce vue-resource correctly. , or there is a problem with the configuration of vue-resource, or we did not correctly use the relevant methods provided by vue-resource, or the code read a null value due to asynchronous operation.

We need to carefully find and eliminate these problems in the code to solve this error message.

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