How to solve 'TypeError: Cannot read property 'yyy' of null' in Vue application?

In the process of developing Vue applications, we may often encounter the error "TypeError: Cannot read property 'yyy' of null". This error is usually caused by accessing the properties of an empty object in our code. Once this error occurs, our application will not be able to run normally, so it needs to be resolved in time.

Common "TypeError: Cannot read property 'yyy' of null" scenarios include:

1. Accessing an uninitialized object or variable

If we forget to initialize objects or variables when using them, we will encounter this error when trying to access their properties. For example:

let obj;
console.log(obj.yyy);
// TypeError: Cannot read property 'yyy' of undefined

The obj here has not been initialized, so the above error will occur when trying to access its yyy property.

2. Operation on a non-existent object or variable

This error will also occur if we operate on a non-existent object or variable. For example:

let obj = null;
console.log(obj.yyy);
// TypeError: Cannot read property 'yyy' of null

In this example, we assign obj to null, which means it does not exist. So the above error occurs when trying to access its yyy property.

3. Using asynchronous requests in components

If we use asynchronous requests to obtain data in a Vue component, it is possible to try to access the data before the request returns. A certain attribute, the above error will occur at this time. For example:

export default {
  data() {
    return {
      user: null
    };
  },
  methods: {
    async getUser() {
      const response = await fetch('https://api.example.com/user');
      const data = await response.json();
      this.user = data;
    }
  },
  mounted() {
    this.getUser();
    console.log(this.user.yyy);
    // TypeError: Cannot read property 'yyy' of null
  }
};

In this example, we call the getUser method in the component's mounted life cycle hook to initiate an asynchronous request, obtain user data and store it in the component in the user attribute. Then, we try to access the yyy attribute of the user object, but since the request has not yet returned, the user attribute is null at this time, so The above error occurred.

There are many ways to solve "TypeError: Cannot read property 'yyy' of null". Let’s take a look at them separately:

1. Initializing uninitialized objects or variables

We should avoid using uninitialized objects or variables as much as possible. If you really need to use it, you should initialize it before using it. For example:

let obj = {};
console.log(obj.yyy);
// undefined

Here, we initialize the obj object to an empty object before using it. This way trying to access its yyy property will result in undefined instead of an error.

2. Checking whether an object or variable exists

Before accessing the properties of an object or variable, we should first check whether they exist. For example:

let obj = null;
if (obj && obj.yyy) {
  console.log(obj.yyy);
} else {
  console.log('obj or obj.yyy does not exist');
}

In this example, we first check whether the obj object exists. If it exists and its yyy attribute also exists, then output ## The value of #obj.yyy. If it does not exist, an error message is output.

Using Vue's conditional rendering

In Vue we can use conditional rendering to render only when the data exists. For example:

<template>
  <div>
    <div v-if="user">
      {{ user.yyy }}
    </div>
    <div v-else>
      User data does not exist.
    </div>
  </div>
</template>

In this example, we use Vue's conditional rendering directive

v-if, which only renders the user data when it exists. The div element of user.yyy. Otherwise, render another div element and display an error message. To sum up, when encountering the error "TypeError: Cannot read property 'yyy' of null", we should first check whether there is property access to the null object in the code, and then choose an appropriate solution. method to repair. This ensures that our Vue application can run smoothly.

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