Network

One of React Native's goals is to be a playground where we can experiment with different architectures and crazy ideas. Since browsers are not flexible enough, we had no choice but to reimplement the entire stack. In the places that we did not intend to change anything, we tried to be as faithful as possible to the browser APIs. The networking stack is a great example.

Fetch

fetch is a better networking API being worked on by the standards committee and is already available in Chrome. It is available in React Native by default.

Usage

fetch('https://mywebsite.com/endpoint/')

Include a request object as the optional second argument to customize the HTTP request:

fetch('https://mywebsite.com/endpoint/', {
  method: 'POST',
  headers: {
    'Accept': 'application/json',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    firstParam: 'yourValue',
    secondParam: 'yourOtherValue',
  })
})

Async

fetch returns a Promise that can be processed in two ways:

1. Using then and catch in synchronous code:

   fetch('https://mywebsite.com/endpoint.php')
   .then((response) => response.text())
   .then((responseText) => {
     console.log(responseText);
   })
   .catch((error) => {
     console.warn(error);
   });

2. Called within an asynchronous function using ES7 async/await syntax:

   class MyComponent extends React.Component {
   ...
   async getUsersFromApi() {
     try {
       let response = await fetch('https://mywebsite.com/endpoint/');
       let responseJson = await response.json();
       return responseJson.users;
     } catch(error) {
       // Handle error
       console.error(error);
     }
   }
   ...
   }

3. Note: Errors thrown by rejected Promises need to be caught, or they will be swallowed silently

WebSocket

WebSocket is a protocol providing full-duplex communication channels over a single TCP connection.

var ws = new WebSocket('ws://host.com/path');

ws.onopen = () => {
  // connection opened
  ws.send('something');
};

ws.onmessage = (e) => {
  // a message was received
  console.log(e.data);
};

ws.onerror = (e) => {
  // an error occurred
  console.log(e.message);
};

ws.onclose = (e) => {
  // connection closed
  console.log(e.code, e.reason);
};

XMLHttpRequest

XMLHttpRequest API is implemented on-top of iOS networking apis and OkHttp. The notable difference from web is the security model: you can read from arbitrary websites on the internet since there is no concept of CORS.

var request = new XMLHttpRequest();
request.onreadystatechange = (e) => {
  if (request.readyState !== 4) {
    return;
  }

  if (request.status === 200) {
    console.log('success', request.responseText);
  } else {
    console.warn('error');
  }
};

request.open('GET', 'https://mywebsite.com/endpoint.php');
request.send();

You can also use -

var request = new XMLHttpRequest();

function onLoad() {
    console.log(request.status);
    console.log(request.responseText);
};

function onTimeout() {
    console.log('Timeout');
    console.log(request.responseText);
};

function onError() {
    console.log('General network error');
    console.log(request.responseText);
};

request.onload = onLoad;
request.ontimeout = onTimeout;
request.onerror = onError;
request.open('GET', 'https://mywebsite.com/endpoint.php');
request.send();

Please follow the MDN Documentation for a complete description of the API.

As a developer, you're probably not going to use XMLHttpRequest directly as its API is very tedious to work with. But the fact that it is implemented and compatible with the browser API gives you the ability to use third-party libraries such as frisbee or axios directly from npm.