The most common way for frontend programs to communicate with servers is through the HTTP protocol. You are probably familiar with the Fetch API and the XMLHttpRequest interface, which allow you fetch resources and make HTTP requests.

If you are using a JavaScript library, chances are it comes with a client HTTP API. jQuery’s $.ajax() function, for example, has been particularly popular with frontend developers. But as developers move away from such libraries in favor of native APIs, dedicated HTTP clients have emerged to fill the gap.

In this post we will take a good look at Axios, a client HTTP API based on the XMLHttpRequest interface provided by browsers, and examine the key features that has contributed to its rise in popularity among frontend developers.

Why Axios?

As with Fetch, Axios is promise-based. However, it provides a more powerful and flexible feature set. Advantages over the native Fetch API include:

• Request and response interception
• Streamlined error handling
• Protection against XSRF
• Support for upload progress
• Response timeout
• The ability to cancel requests
• Support for older browsers
• Automatic JSON data transformation

Installation

You can install Axios using:

• npm:

  $ npm install axios

• The Bower package manager:

  $ bower install axios

• Or a content delivery network:

  <script src="https://unpkg.com/axios/dist/axios.min.js"></script>

Making requests

Making an HTTP request is as easy as passing a config object to the Axios function. In its simplest form, the object must have a url property; if no method is provided, GET will be used as the default value. Let’s look at a simple example:

// send a POST request
axios({
  method: 'post',
  url: '/login',
  data: {
    firstName: 'Finn',
    lastName: 'Williams'
  }
});

This should look familiar to those who have worked with jQuery’s $.ajax function. This code is simply instructing Axios to send a POST request to /login with an object of key/value pairs as its data. Axios will automatically convert the data to JSON and send it as the request body.

Shorthand methods

Axios also provides a set of shorthand methods for performing different types of requests. The methods are as follows:

• axios.request(config)
• axios.get(url[, config])
• axios.delete(url[, config])
• axios.head(url[, config])
• axios.options(url[, config])
• axios.post(url[, data[, config]])
• axios.put(url[, data[, config]])
• axios.patch(url[, data[, config]])

For instance, the following code shows how the previous example could be written using the axios.post() method:

axios.post('/login', {
  firstName: 'Finn',
  lastName: 'Williams'
});

Handling the response

Once an HTTP request is made, Axios returns a promise that is either fulfilled or rejected, depending on the response from the backend service. To handle the result, you can use the then() method like this:

axios.post('/login', {
  firstName: 'Finn',
  lastName: 'Williams'
})
.then((response) => {
  console.log(response);
}, (error) => {
  console.log(error);
});

If the promise is fulfilled, the first argument of then() will be called; if the promise is rejected, the second argument will be called. According to the documentation, the fulfillment value is an object containing the following information:

{
  // `data` is the response that was provided by the server
  data: {},
 
  // `status` is the HTTP status code from the server response
  status: 200,
 
  // `statusText` is the HTTP status message from the server response
  statusText: 'OK',
 
  // `headers` the headers that the server responded with
  // All header names are lower cased
  headers: {},
 
  // `config` is the config that was provided to `axios` for the request
  config: {},
 
  // `request` is the request that generated this response
  // It is the last ClientRequest instance in node.js (in redirects)
  // and an XMLHttpRequest instance the browser
  request: {}
}

As an example, here’s how the response looks when requesting data from the GitHub API:

axios.get('https://api.github.com/users/mapbox')
  .then((response) => {
    console.log(response.data);
    console.log(response.status);
    console.log(response.statusText);
    console.log(response.headers);
    console.log(response.config);
  });

// logs:
// => {login: "mapbox", id: 600935, node_id: "MDEyOk9yZ2FuaXphdGlvbjYwMDkzNQ==", avatar_url: "https://avatars1.githubusercontent.com/u/600935?v=4", gravatar_id: "", …}
// => 200
// => OK
// => {x-ratelimit-limit: "60", x-github-media-type: "github.v3", x-ratelimit-remaining: "60", last-modified: "Wed, 01 Aug 2018 02:50:03 GMT", etag: "W/"3062389570cc468e0b474db27046e8c9"", …}
// => {adapter: ƒ, transformRequest: {…}, transformResponse: {…}, timeout: 0, xsrfCookieName: "XSRF-TOKEN", …}

Making simultaneous requests

One of Axios’ more interesting features is its ability to make multiple requests in parallel by passing an array of arguments to the axios.all() method. This method returns a single promise object that resolves only when all arguments passed as an array have resolved. Here’s a simple example:

// execute simultaneous requests 
axios.all([
  axios.get('https://api.github.com/users/mapbox'),
  axios.get('https://api.github.com/users/phantomjs')
])
.then(responseArr => {
  //this will be executed only when all requests are complete
  console.log('Date created: ', responseArr[0].data.created_at);
  console.log('Date created: ', responseArr[1].data.created_at);
});

// logs:
// => Date created:  2011-02-04T19:02:13Z
// => Date created:  2017-04-03T17:25:46Z

This code makes two requests to the GitHub API and then logs the value of the created_at property of each response to the console. Keep in mind that if any of the arguments rejects then the promise will immediately reject with the reason of the first promise that rejects.

For convenience, Axios also provides a method called axios.spread() to assign the properties of the response array to separate variables. Here’s how you could use this method:

axios.all([
  axios.get('https://api.github.com/users/mapbox'),
  axios.get('https://api.github.com/users/phantomjs')
])
.then(axios.spread((user1, user2) => {
  console.log('Date created: ', user1.data.created_at);
  console.log('Date created: ', user2.data.created_at);
}));

// logs:
// => Date created:  2011-02-04T19:02:13Z
// => Date created:  2017-04-03T17:25:46Z

The output of this code is the same as the previous example. The only difference is that the axios.spread() method is used to unpack values from the response array.

Sending custom headers

Sending custom headers with Axios is very straightforward. Simply pass an object containing the headers as the last argument. For example:

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const options = {
  headers: {'X-Custom-Header': 'value'}
};

axios.post('/save', { a: 10 }, options);

Transforming requests and responses

By default, Axios automatically converts requests and responses to JSON. But it also allows you to override the default behavior and define a different transformation mechanism. This ability is particularly useful when working with an API that accepts only a specific data format such as XML or CSV.

To change the request data before sending it to the server, set the transformRequest property in the config object. Note that this method only works for PUT, POST, and PATCH request methods. Here’s how you can do that:

const options = {
  method: 'post',
  url: '/login',
  data: {
    firstName: 'Finn',
    lastName: 'Williams'
  },
  transformRequest: [(data, headers) => {
    // transform the data

    return data;
  }]
};

// send the request
axios(options);

To modify the data before passing it to then() or catch(), you can set the transformResponse property:

const options = {
  method: 'post',
  url: '/login',
  data: {
    firstName: 'Finn',
    lastName: 'Williams'
  },
  transformResponse: [(data) => {
    // transform the response

    return data;
  }]
};

// send the request
axios(options);

Intercepting requests and responses

HTTP Interception is a popular feature of Axios. With this feature, you can examine and change HTTP requests from your program to the server and vice versa, which is very useful for a variety of implicit tasks, such as logging and authentication.

At first glance, interceptors look very much like transforms, but they differ in one key way: unlike transforms, which only receive the data and headers as arguments, interceptors receive the entire response object or request config.

You can declare a request interceptor in Axios like this:

// declare a request interceptor
axios.interceptors.request.use(config => {
  // perform a task before the request is sent
  console.log('Request was sent');

  return config;
}, error => {
  // handle the error
  return Promise.reject(error);
});

// sent a GET request
axios.get('https://api.github.com/users/mapbox')
  .then(response => {
    console.log(response.data.created_at);
  });

This code logs a message to the console whenever a request is sent then waits until it gets a response from the server, at which point it prints the time the account was created at GitHub to the console. One advantage of using interceptors is that you no longer have to implement tasks for each HTTP request separately.

Axios also provides a response interceptor, which allows you to transform the responses from a server on their way back to the application:

// declare a response interceptor
axios.interceptors.response.use((response) => {
  // do something with the response data
  console.log('Response was received');

  return response;
}, error => {
  // handle the response error
  return Promise.reject(error);
});

// sent a GET request
axios.get('https://api.github.com/users/mapbox')
  .then(response => {
    console.log(response.data.created_at);
  });

Client-side support for protection against XSRF

Cross-site request forgery (or XSRF for short) is a method of attacking a web-hosted app in which the attacker disguises himself as a legal and trusted user to influence the interaction between the app and the user’s browser. There are many ways to execute such an attack, including XMLHttpRequest.

Fortunately, Axios is designed to protect against XSRF by allowing you to embed additional authentication data when making requests. This enables the server to discover requests from unauthorized locations. Here’s how this can be done with Axios:

const options = {
  method: 'post',
  url: '/login',
  xsrfCookieName: 'XSRF-TOKEN',
  xsrfHeaderName: 'X-XSRF-TOKEN',
};

// send the request
axios(options);

Monitoring POST request progress

Another interesting feature of Axios is the ability to monitor request progress. This is especially useful when downloading or uploading large files. The provided example in the Axios documentation gives you a good idea of how that can be done. But for the sake of simplicity and style, we are going to use the Axios Progress Bar module in this tutorial.

The first thing we need to do to use this module is to include the related style and script:

<link rel="stylesheet" type="text/css" href="https://cdn.rawgit.com/rikmms/progress-bar-4-axios/0a3acf92/dist/nprogress.css" />

<script src="https://cdn.rawgit.com/rikmms/progress-bar-4-axios/0a3acf92/dist/index.js"></script>

Then we can implement the progress bar like this:

loadProgressBar()

const url = 'https://media.giphy.com/media/C6JQPEUsZUyVq/giphy.gif';

function downloadFile(url) {
  axios.get(url)
  .then(response => {
    console.log(response)
  })
  .catch(error => {
    console.log(error)
  })
}

downloadFile(url);

To change the default styling of the progress bar, we can override the following style rules:

#nprogress .bar {
    background: red !important;
}

#nprogress .peg {
    box-shadow: 0 0 10px red, 0 0 5px red !important;
}

#nprogress .spinner-icon {
    border-top-color: red !important;
    border-left-color: red !important;
}

Canceling requests

In some situations, you may no longer care about the result and want to cancel a request that’s already sent. This can be done by using a cancel token. The ability to cancel requests was added to Axios in version 1.5 and is based on the cancelable promises proposal. Here’s a simple example:

const source = axios.CancelToken.source();

axios.get('https://media.giphy.com/media/C6JQPEUsZUyVq/giphy.gif', {
  cancelToken: source.token
}).catch(thrown => {
  if (axios.isCancel(thrown)) {
    console.log(thrown.message);
  } else {
    // handle error
  }
});

// cancel the request (the message parameter is optional)
source.cancel('Request canceled.');

You can also create a cancel token by passing an executor function to the CancelToken constructor, as shown below:

const CancelToken = axios.CancelToken;
let cancel;

axios.get('https://media.giphy.com/media/C6JQPEUsZUyVq/giphy.gif', {
  // specify a cancel token
  cancelToken: new CancelToken(c => {
    // this function will receive a cancel function as a parameter
    cancel = c;
  })
}).catch(thrown => {
  if (axios.isCancel(thrown)) {
    console.log(thrown.message);
  } else {
    // handle error
  }
});

// cancel the request
cancel('Request canceled.');

Libraries

Axios’ rise in popularity among developers has resulted in a rich selection of third-party libraries that extend its functionality. From testers to loggers, there’s a library for almost any additional feature you may need when using Axios. Here are some popular libraries currently available:

• axios-vcr: 📼 Record and replay requests in JavaScript
• axios-response-logger: 📣 Axios interceptor which logs responses
• axios-method-override: ⛵️ Axios request method override plugin
• axios-extensions: 🍱 Axios extensions lib, including throttle and cache GET request features
• axios-api-versioning: Add easy-to-manage API versioning to Axios
• axios-cache-plugin: Helps you cache GET requests when using Axios
• axios-cookiejar-support: Add tough-cookie support to Axios
• react-hooks-axios: Custom React Hooks for Axios
• moxios: Mock Axios requests for testing
• redux-saga-requests: Redux-Saga add-on to simplify handling of AJAX requests
• axios-fetch: A Web API Fetch implementation backed by an Axios client
• axios-curlirize: Log any Axios request as a curl command in the console
• axios-actions: Bundle endpoints as callable, reusable services
• mocha-axios: HTTP assertions for Mocha using Axios
• axios-mock-adapter: Axios adapter that allows you to easily mock requests
• axios-debug-log: Axios interceptor of logging request and response with debug library
• redux-axios-middleware: Redux middleware for fetching data with Axios HTTP client
• axiosist: Axios-based supertest: convert nNode.js request handler to Axios adapter, used for Node.js server unit test

Browser support

When it comes to browser support, Axios is very reliable. Even older browsers such as IE 11 work well with Axios.

Chrome	Firefox	Safari	Edge	IE
				11

Wrapping up

There’s a good reason Axios is so popular among developers: it’s packed with useful features. In this post, we’ve taken a good look at several key features of Axios and learned how to use them in practice. But there are still many aspects of Axios that we’ve not discussed. So be sure to check out the Axios GitHub page to learn more.

Do you have some tips on using Axios? Let us know in the comments!

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