Networking Guide

Summary:
Simplified Networking Guide, based on the old Network polyfill doc.

This guide strongly recommends using fetch, while still informing the user about React Native's support for other libraries.

In order to provide an actual working networking example, a `movies.json` file is added at the root of the site, allowing the user to fetch a small blob of JSON:

```
fetch('http://facebook.github.io/react-native/movies.json')
```

![networking](https://cloud.githubusercontent.com/assets/165856/16321804/d2bd7c6a-3953-11e6-9fc5-30baaa38d7a4.png)
Closes facebook#8381

Differential Revision: D3479018

Pulled By: lacker

fbshipit-source-id: 1f2078bf2414a13f7f77d5af55b08948909093a3

Author: hramos

docs/Basics-Network.md

@@ -1,25 +1,27 @@
 ---
 id: basics-network
-title: Network
+title: Networking
 layout: docs
 category: The Basics
 permalink: docs/network.html
 next: more-resources
 ---
 
-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.
+Many mobile apps need to load resources from a remote URL. You may want to make a POST request to a REST API, or you may simply need to fetch a chunk of static content from another server.
 
-## Fetch
+## Using Fetch
 
-[fetch](https://fetch.spec.whatwg.org/) 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.
+React Native provides the [Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API) for your networking needs. Fetch will seem familiar if you have used `XMLHttpRequest` or other networking APIs before. You may refer to MDN's guide on [Using Fetch](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch) for additional information.
 
-#### Usage
+#### Making requests
+
+In order to fetch content from an arbitrary URL, just pass the URL to fetch:
 
 ```js
-fetch('https://mywebsite.com/endpoint/')
+fetch('https://mywebsite.com/mydata.json')
 ```
 
-Include a request object as the optional second argument to customize the HTTP request:
+Fetch also takes an optional second argument that allows you to customize the HTTP request. You may want to specify additional headers, or make a POST request:
 
 ```js
 fetch('https://mywebsite.com/endpoint/', {
@@ -35,74 +37,46 @@ fetch('https://mywebsite.com/endpoint/', {
 })
 ```
 
-#### Async
+Take a look at the [Fetch Request docs](https://developer.mozilla.org/en-US/docs/Web/API/Request) for a full list of properties.
+
+#### Handling the response
 
-`fetch` returns a [Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) that can be processed in two ways:
+The above examples show how you can make a request. In many cases, you will want to do something with the response.
 
-1.  Using `then` and `catch` in synchronous code:
+Networking is an inherently asynchronous operation. Fetch methods will return a  [Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) that make it straightforward to write code that works in an asynchronous manner:
 
   ```js
-  fetch('https://mywebsite.com/endpoint.php')
-    .then((response) => response.text())
-    .then((responseText) => {
-      console.log(responseText);
-    })
-    .catch((error) => {
-      console.warn(error);
-    });
+  getMoviesFromApiAsync() {
+    return fetch('http://facebook.github.io/react-native/movies.json')
+      .then((response) => response.json())
+      .then((responseJson) => {
+        return responseJson.movies;
+      })
+      .catch((error) => {
+        console.error(error);
+      });
+  }
   ```
-2.  Called within an asynchronous function using ES7 `async`/`await` syntax:
+
+You can also use ES7's `async`/`await` syntax in React Native app:
 
   ```js
-  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);
-      }
+  async getMoviesFromApi() {
+    try {
+      let response = await fetch('http://facebook.github.io/react-native/movies.json');
+      let responseJson = await response.json();
+      return responseJson.movies;
+    } catch(error) {
+      console.error(error);
     }
-    ...
   }
   ```
 
-- Note: Errors thrown by rejected Promises need to be caught, or they will be swallowed silently
+Don't forget to catch any errors that may be thrown by `fetch`, otherwise they will be dropped silently.
 
-## WebSocket
+### Using Other Networking Libraries
 
-WebSocket is a protocol providing full-duplex communication channels over a single TCP connection.
-
-```js
-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](https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/URLLoadingSystem/URLLoadingSystem.html) and [OkHttp](http://square.github.io/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](http://en.wikipedia.org/wiki/Cross-origin_resource_sharing).
+The [XMLHttpRequest API](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest) is built in to React Native. This means that you can use third party libraries such as [frisbee](https://github.com/niftylettuce/frisbee) or [axios](https://github.com/mzabriskie/axios) that depend on it, or you can use the XMLHttpRequest API directly if you prefer.
 
 ```js
 var request = new XMLHttpRequest();
@@ -118,38 +92,36 @@ request.onreadystatechange = (e) => {
   }
 };
 
-request.open('GET', 'https://mywebsite.com/endpoint.php');
+request.open('GET', 'https://mywebsite.com/endpoint/');
 request.send();
 ```
 
-You can also use -
+> The security model for XMLHttpRequest is different than on web as there is no concept of [CORS](http://en.wikipedia.org/wiki/Cross-origin_resource_sharing) in native apps.
+
+## WebSocket Support
+
+React Native supports [WebSocket](https://developer.mozilla.org/en-US/docs/Web/API/WebSocket), a protocol which provides full-duplex communication channels over a single TCP connection.
 
 ```js
-var request = new XMLHttpRequest();
+var ws = new WebSocket('ws://host.com/path');
 
-function onLoad() {
-    console.log(request.status);
-    console.log(request.responseText);
+ws.onopen = () => {
+  // connection opened
+  ws.send('something');
 };
 
-function onTimeout() {
-    console.log('Timeout');
-    console.log(request.responseText);
+ws.onmessage = (e) => {
+  // a message was received
+  console.log(e.data);
 };
 
-function onError() {
-    console.log('General network error');
-    console.log(request.responseText);
+ws.onerror = (e) => {
+  // an error occurred
+  console.log(e.message);
 };
 
-request.onload = onLoad;
-request.ontimeout = onTimeout;
-request.onerror = onError;
-request.open('GET', 'https://mywebsite.com/endpoint.php');
-request.send();
+ws.onclose = (e) => {
+  // connection closed
+  console.log(e.code, e.reason);
+};
 ```
-
-
-Please follow the [MDN Documentation](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest) 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](https://github.com/niftylettuce/frisbee) or [axios](https://github.com/mzabriskie/axios) directly from npm.

website/src/react-native/movies.json

@@ -0,0 +1,11 @@
+{
+  "title": "The Basics - Networking",
+  "description": "Your app fetched this from a remote endpoint!",
+  "movies": [
+    { "title": "Star Wars", "releaseYear": "1977"},
+    { "title": "Back to the Future", "releaseYear": "1985"},
+    { "title": "The Matrix", "releaseYear": "1999"},
+    { "title": "Inception", "releaseYear": "2010"},
+    { "title": "Interstellar", "releaseYear": "2014"}
+  ]
+}