What should I do if 'Uncaught (in promise) Error: Request failed with status code 400' occurs when using axios in a Vue application?

Using axios as the network request framework in Vue applications, processing data usually involves communicating with the back-end API. However, in some cases, we may encounter an error i.e. "Uncaught (in promise) Error: Request failed with status code 400". This error usually occurs when requesting an API, indicating that the request has been sent, but the server cannot process the request due to incorrect data format or incorrect parameters.

How to deal with this error? Below we'll cover a few possible solutions.

1. Check the URL and parameters of the API request

First, we need to check the URL and parameters of the API request to ensure that they meet the requirements of the API. This problem is usually caused by incorrect parameters or wrong URLs being provided when requesting the API, causing the server to be unable to process the request.

You can use the Chrome browser's development tools to view the requested URL and parameters to check whether they are correct.

2. Set the axios request header file

In Vue applications, we usually use the axios plug-in to send HTTP requests. If you need to set specific parameters or header files in the request header when requesting the API, then we need to ensure that the request header is set correctly in the axios plugin.

axios.defaults.headers.common['Authorization'] = 'Bearer ' token;

In the above code, we set a request header to attach the Bearer token to Authorization .

3. Send the correct data format when requesting the API

In applications, the data type we are familiar with is JSON. When processing data in a Vue application, we need to ensure that the data is sent to the server in JSON format. If we send data in other formats (for example, form data or XML format data), the server may return a 400 error.

Use the Content-Type: application/json header to ensure the data is sent in JSON format. The following is an example of sending data objects to the backend API in JSON format.

let data = { name: 'John', age: 30 };
axios.post('/api/user', JSON.stringify(data), { headers: { 'Content-Type ': 'application/json' } });

4. Catch errors and display error messages

We can use axios response interceptor to capture errors and display error messages. In a Vue application, we can create an axios instance in the main.js file and add a response interceptor.

In the following code snippet, we add a response interceptor on the axios instance. When a request error occurs, the response interceptor's error handler is called and the error message is displayed.

import axios from 'axios';
import Vue from 'vue';

let instance = axios.create({
baseURL: 'http://localhost:3000 ',
timeout: 30000
});

instance.interceptors.response.use(function (response) {
return response;
}, function (error) {
Vue.prototype.$message.error(error.message);
return Promise.reject(error);
});

In the above code snippet, we use Vue’s $message instance to display error messages.

Summary

In Vue applications, we usually use axios as the network request library. When requesting the API, we may encounter the "Uncaught (in promise) Error: Request failed with status code 400" error. This error usually indicates that we need to check the URL, parameters, request headers and data format of the API request.

When solving this problem, we can troubleshoot the problem by checking the URL and parameters of the API request, setting the request header file of axios, sending the correct data format, and capturing errors and displaying error messages.

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