axios

Axios HTTP Client

Axios is a promise-based HTTP client for the browser and Node.js. It provides a simple API for making HTTP requests and handling responses.

Quick Start

Basic GET Request

import axios from "axios";

// Promise-based
axios
  .get("/user?ID=12345")
  .then((response) => console.log(response.data))
  .catch((error) => console.error(error));

// Async/await
async function getUser() {
  try {
    const response = await axios.get("/user?ID=12345");
    console.log(response.data);
  } catch (error) {
    console.error(error);
  }
}

Basic POST Request

axios
  .post("/user", {
    firstName: "John",
    lastName: "Doe",
  })
  .then((response) => console.log(response.data))
  .catch((error) => console.error(error));

Common Patterns

Custom Instance

const api = axios.create({
  baseURL: "https://api.example.com",
  timeout: 1000,
  headers: { "X-Custom-Header": "foobar" },
});

// Use the instance
api.get("/users").then((response) => console.log(response.data));

Request with Configuration

axios({
  method: "post",
  url: "/user/12345",
  data: {
    firstName: "Fred",
    lastName: "Flintstone",
  },
  headers: {
    "Content-Type": "application/json",
    Authorization: "Bearer token",
  },
});

Concurrent Requests

function getUserAccount() {
  return axios.get("/user/12345");
}

function getUserPermissions() {
  return axios.get("/user/12345/permissions");
}

Promise.all([getUserAccount(), getUserPermissions()]).then(
  ([account, permissions]) => {
    console.log("Account:", account.data);
    console.log("Permissions:", permissions.data);
  },
);

Error Handling

Basic Error Handling

axios.get("/user/12345").catch(function (error) {
  if (error.response) {
    // Server responded with error status
    console.log(error.response.data);
    console.log(error.response.status);
    console.log(error.response.headers);
  } else if (error.request) {
    // Request was made but no response received
    console.log(error.request);
  } else {
    // Error in request setup
    console.log("Error", error.message);
  }
});

Custom Error Status Validation

axios.get("/user/12345", {
  validateStatus: function (status) {
    return status < 500; // Resolve only if status < 500
  },
});

Interceptors

Request Interceptor

axios.interceptors.request.use(
  (config) => {
    // Add auth token to headers
    const token = localStorage.getItem("token");
    if (token) {
      config.headers.Authorization = `Bearer ${token}`;
    }
    return config;
  },
  (error) => {
    return Promise.reject(error);
  },
);

Response Interceptor

axios.interceptors.response.use(
  (response) => {
    // Transform response data
    return response.data;
  },
  (error) => {
    // Handle common errors
    if (error.response?.status === 401) {
      // Redirect to login
      window.location.href = "/login";
    }
    return Promise.reject(error);
  },
);

Authentication Retry Pattern

const api = axios.create({ baseURL: "/api" });

api.interceptors.response.use(undefined, async (error) => {
  if (error.response?.status === 401) {
    await refreshToken();
    return api(error.config); // Retry original request
  }
  throw error;
});

Request/Response Configuration

Common Configuration Options

const config = {
  url: "/user",
  method: "get",
  baseURL: "https://api.example.com",
  headers: { "X-Requested-With": "XMLHttpRequest" },
  params: { ID: 12345 },
  data: { firstName: "John" },
  timeout: 5000,
  responseType: "json",
  withCredentials: false,
  validateStatus: (status) => status >= 200 && status < 300,
};

FormData Upload

const formData = new FormData();
formData.append("file", fileInput.files[0]);
formData.append("username", "john");

axios.post("/upload", formData, {
  headers: {
    "Content-Type": "multipart/form-data",
  },
});

Download Progress

axios.get("/download/file", {
  onDownloadProgress: (progressEvent) => {
    const percentCompleted = Math.round(
      (progressEvent.loaded * 100) / progressEvent.total,
    );
    console.log(`Download: ${percentCompleted}%`);
  },
});

Response Schema

Axios responses contain:

{
  data: {}, // Server response data
  status: 200, // HTTP status code
  statusText: 'OK', // HTTP status message
  headers: {}, // Response headers
  config: {}, // Request config
  request: {} // Request object
}

Best Practices

1. Use instances for different APIs or configurations
2. Implement interceptors for auth, logging, and error handling
3. Set timeouts to prevent hanging requests
4. Handle errors at appropriate levels
5. Use TypeScript for better type safety
6. Cancel requests when components unmount

TypeScript Support

import axios, { AxiosResponse } from "axios";

interface User {
  id: number;
  name: string;
  email: string;
}

const response: AxiosResponse<User> = await axios.get<User>("/user/123");
const user: User = response.data;