What should I do if 'Cannot read property 'xxx' of undefined' appears when using axios in a Vue application?

In Vue applications, we often use the axios library to realize the interaction between the front end and the back end, such as sending requests to the background to obtain data. However, when using axios, we may encounter errors similar to "Cannot read property 'xxx' of undefined". This error message is relatively broad, and the error message is different for different reasons.

In this article, we will introduce what may cause this error and how to solve it.

1. Reason

When using the axios library to request data in a Vue application, the reasons for encountering the "Cannot read property 'xxx' of undefined" error may be as follows:

1. axios has not been introduced or is not installed correctly

If the axios dependent library is not correctly installed in our Vue application, or axios is not correctly introduced in the component, then when we call axios , the system will prompt the error Cannot read property 'xxx' of undefined.

2. Use an attribute in data before rendering of incomplete data data is completed

Since the Vue application framework uses the feature of two-way data binding, when using arrows When a function or callback function is used to modify the value of a variable, a temporary variable will be generated. When some developers use this temporary variable, because they do not know whether the attributes in the data are rendered successfully, the error message will appear.

3. Asynchronous requests cause variables to be unable to be obtained in time

Since axios requests in Vue applications are executed asynchronously, some developers do not handle asynchronous data correctly. Processing, causing the variable's object to be empty. When this variable is empty, a Cannot read property 'xxx' of undefined error will occur when calling its properties.

2. Solution

If this problem occurs, you can try the following solution:

1. Confirm whether the axios dependent library is installed correctly. If it is not installed, Or if you are not sure whether it is installed, you can execute the following command in the project root directory to install it:

npm install axios --save

2. Confirm whether the axios library is correctly introduced in the component and call axios correctly when needed. method.
3. It is recommended to use arrow functions to access the value of data variables to avoid problems with temporary variables.
4. When using asynchronous requests, you can use Promise or async/await syntax to put the content of the asynchronous request into a callback function for execution to ensure that the object can obtain the appropriate value.

// Promise对象
new Promise((resolve, reject) => {
  axios.get('/api/data')
    .then((res) => {
      resolve(res)
    })
    .catch((error) => {
      reject(error)
    })
})

// async/await语法
async function fetchData () {
  try {
    const res = await axios.get('/api/data')
    return res
  } catch (error) {
    console.log(error)
  }
}

Summary

The Cannot read property 'xxx' of undefined error occurs when using axios in a Vue application. This may be due to incorrect installation of dependencies, incorrect introduction of the axios library, This is caused by the use of an attribute in the data before the completion of rendering of incomplete data and the incorrect handling of variables when processing asynchronous requests. We can avoid this by confirming whether the axios library is introduced and called normally and using Promise or async/await syntax. Error occurs.

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